Paragraph 3

ἐπεὶ δὲ προσχωρεῖ τῷ κήπῳ, .....

ἐν ᾧ δέ = while, at the same time
ἐν ᾧ δὲ πονεῖ, στενάζει
ε͂πεὶ δέ = 1. when = after
ε͂πεὶ δέ = 2. because, since
Context will usually tell us which meaning to choose in a given sentence.
ἐπεὶ δὲ ὁρᾷ τὸν λίθον, στενάζει.
When he sees the stone, he moans.

ἐπεὶ δὲ ἀθυμεῖ, καλεῖ τὸν πατέρα
Because/Since/As he despairs, he calls his dad.
or: When he despairs.... meaning: When he really feels at the end of his tether he calls his father for help.
ἐπεὶ δὲ λίθοι μεγάλοι τὸν ἄροτον ἐμποδίζουσιν, ἀθυμεῖ ὁ δοῦλος καὶ μέγα στενάζει.
Since big stones are hindering their plowing, the slave despairs and moans loudly.
ἐπεὶ δὲ προσχωρεῖ τῷ ἀγρῷ, ὁρᾷ λαγὼν ταχέως τρέχοντα.
When he approaches the field, he sees a hare running quickly.
 

πόθεν ἥκεις καὶ ποῦ ἐστιν ὁ Ἄργος;

πόθεν; from where? movement away from, out of, from
We have already seen the -θεν suffix in ὄπισθεν (behind): βαδίζει ὄπισθεν τοῦ ἀρότρου
ποῦ; where (is)? Position: the dog is asleep: in the room on the floor under the table (all dative case-form endings)
ποῖ; where to? Movement towards: in the direction of the mountains, into the field
πόθεν ἥκει ὁ Δικαιόπολις; ἀπὸ τοῦ ἀγροῦ
ποῖ βαδίζει; πρὸς τὸν οἶκον
ποῦ ἐστιν ἡ Μυρρίνη; ἐν τῷ οἴκῳ
πόθεν ἥκει ἡ Μέλιττα; Remember that she had to go and get a new water jar, so
ἥκει ἀπὸ τῆς κρήνης
πόθεν ἥκει ὁ ἄγγελος in lesson 4?
ἥκει ἀπὸ τῶν Ἀθηνῶν
πόθεν ἥκει ὁ Φίλιππος; ἀπὸ τοῦ αὐλίου
 

ὁ δὲ Ἄργος ἐστί που ἐν τοῖς ὄρεσιν.

Important distinction:

• ποῦ where (is)? interrogative, question word
  Question words are always emphasized in speech and are therefore always marked in writing by either an acute (on short syllable) or a circumflex (on long final syllable). Always. Never grave, tone always goes up on a question word in Greek.
  τίς ἥκει;           Who comes?
  τί λέγεις;         What do you say?
  τί ἀθυμεῖς;      Why do you despair?
  πόθεν ἥκεις;   Whither have you come?
  ποῦ πονεῖ ὁ δοῦλος; Where does the slave work?
• Now here we have an unaccented που meaning, not *where?*, but *somewhere*.
  Indefinite adjectives (some, any, no ... man, beast or thing),
  indefinite pronouns (someone, something) and
  indefinite adverbs (somewhere, somehow)
  are enclitics and are only accented when followed by other enclitics that will lean on them.
  When accented they are always accented on the last syllable, while question words are accented on the first. Always. Never grave, tone always goes up on a question word in Greek, pitch rising, or fluctuating incredulously. Like in English when we're surprised or shocked: What? Who? Where?

Examples:
ποῦ ἐστιν ὁ κύων; ἐστί που ἐν τοῖς ὄρεσιν. (somewhere in the hills)
ποῦ εἰσιν οἱ παῖδες; εἰσί που ἐν τῷ κήπῳ. (somewhere in the garden, playing hide-and-seek)
τίς ἥκει; ἄγγελός τις (Who's come? Some messenger.)
τί ποιεῖ ὁ δοῦλος ἐν τῷ κήπῳ; ζητεῖ τι (What's the slave doing in the garden? He's looking for something.)
 

ἴθι δή, ὦ παῖ· τί οὐ ζητεῖς αὐτόν;

When we've lost something or don't know where something is, we look for it: ζητοῦμεν [ζητέομεν] αὐτό.
And what does Philip do?:
οὐχ ὁρᾷ τὸν Ἄργον, μέγα βοᾷ καὶ καλεῖ,
ἀλλὰ ὁ κύων οὐκ ἀκούει.
What should he be doing? Tell him:
ζήτει [ζήτε-ε] τὸν κύνα, ὦ Φίλιππε.
τί οὐ ζητεῖ ὁ παῖς τὸν κύνα; ἐστι που ἐν τοῖς ὄρεσι, τὰ δὲ ὄρη μεγάλα εστίν. χαλεπόν ἐστι ζητεῖν τὸν κύνα ἐν ὄρεσιν οὕτω μεγάλοις. ἀθυμεῖ οὖν ὁ παῖς καὶ οἰκαδε βαδίζει.
 
 Pattern: 
Why don't you....? and: So, why don't you....?
(διὰ) τί οὐ καλεῖς τὸν κύνα;   - οὐκ ἀκούει. (it/he doesn't listen)
τί οὖν οὐ βοᾷς; (if just calling is not good enough οὐ ἱκανόν ἐστιν.)   - βοῶ, μέγα βοῶ, ἀλλ' ἔτι καὶ νῦν οὐκ ἀκούει ὁ κατάρατος.
τρέχει; τί οὖν οὐ τρέχεις μετ' αὐτόν;   - οὕτω ταχέως τρέχει, ὥσπερ οὐ δυνατόν ἐστι διώκειν αὐτόν. ἐγὼ μὲν οὖν τρέχειν οὐκ ἐθέλω. μάλα γὰρ κάμνω, καὶ δε καὶ (moreover) φλέγει ὁ ἥλιος καὶ κατατρίβει ἐμέ. οὐ κάμνεις καὶ σύ;
οὐχ ὁρᾷς τοὺς βοῦς; τί οὖν οὐ ζητεῖς αὐτούς;   - μάλα κάμνω. τί οὐ σύ ζητεῖς αὐτούς;
 

μὴ οὕτω ῥᾴθυμος ἴσθι

•  Note the difference between: 
  ἴθι δή = go on!
  ἴσθι = be! (be good, be brave, be an angel!)
• ῥᾴθυμος, ῥᾴθυμον: the ῥᾴ is short for ῥᾴδιος, ῥᾳδίᾱ, ῥᾴδιον = easy. Remember chapter 4b, when Melitta proudly announces that persuading daddy to take them to the festival is not difficult at all, but easy peasy:
  οὐ χαλεπόν ἐστιν πείθειν τὸν πατέρα, μάλα ῥᾴδιόν ἐστιν.
  And we discussed the θυμός part in paragraph 2.
  So ῥᾴθυμος means light-minded, light-hearted, easy-going and ..... nonchalant, lazy
  In the 1st version ῥᾴθυμος is used instead of ἀργός right from chapter 2, in the description of the slave who is both ῥᾴθυμος (easy-going) and ἀργός (bone-idle). Note that both are compounds and therefore have no 1st declension feminine forms.

 

τί οὖν λέγει ὁ Φίλιππος· οὐ ῥᾴθυμός εἰμι οὐδὲ αἴτιος ἐγώ.

- διότι μέγα βοᾷ καὶ καλεῖ.
- διότι οὐκ ἀκούει ὁ Ἄργος ἀλλὰ ἔτι διώκει τὸν λαγών.
- διότι καὶ ὁ κύων, καὶ ὁ λαγώς ταχέως τρέχουσιν.
- διότι τρέχει μετ' αὐτούς, ἀλλὰ οὕτω ταχέως τρέχουσιν, ὥστε ἤδη οὐ δυνατόν εστιν ὁρᾶν αὐτούς.
He tried hard, but to no avail.
 

οὕτω λέγει καὶ τὴν βακτηρίαν λαμβάνει καὶ ....

οὔτω λέγει. What does the οὕτω refer to?
What does he grab? τὴν βακτηρίαν (his stick of course). Grandfather is old, so he'll need a stick: λαμβάνει οὖν τὴν βακτηρίαν ὥστε ἀναβαίνειν τὴν ὁδόν, εἰς ἀκρὸν τὸ ὄρος.
In the 1st edition it doesn't say τὴν βακτηρίαν ἀλλὰ τὸ βάκτρον for "staff, stick". Both are correct, but ἡ βακτηρία gave us bacteria (because some of them are stick-shape), while τὸ βάκτρον gave us nothing that I can think of, etymology-wise.
Grandfather is old, so he'll need a stick: λαμβάνει οὖν τὴν βακτηρίαν ὥστε ἀναβαίνειν τὴν ὁδόν, εἰς ἄκρον τὸ ὄρος.
 

οὕτω λέγει καὶ τὴν βακτηρίαν λαμβάνει καὶ σπεύδει ἅμα τῷ παιδὶ ἀνὰ τὴν ὁδόν.

ἅμα + dative case form: "together with"
ἅμα alone we had in chapter 3a:
ἅμα οὖν ὅ τε δεσπότης καὶ ὁ δοῦλος αἴρουσι τὸν λίθον καὶ φέρουσιν αὐτὸν ἐκ τοῦ ἀγροῦ.
ὁ μὲν Φίλιππος sets out on his walk ἅμα τῷ κυνί, ὁ δὲ [κύων] disappears ἅμα τῷ λαγῴ.
So now: ὁ οὖν πάππος ζητεῖ τὸν Ἄργον ἅμα τῷ Φιλίππῳ
And as in paragraph 2
ὁ Φίλιππος καταβαίνει τὸ ὄρος
ὁ Φίλιππος καταβαίνει τὴν ὁδόν
now
ὁ παῖς, ἅμα τῷ πάππῳ, σπεύδει ἀνὰ τὴν ὁδόν
ὁ παῖς, ἅμα τῷ πάππῳ, σπεύδει ἀνὰ τὸ ὄρος.
I hope everyone knows κατά, ἀνά, τὸ ὄρος and ἡ ὁδός by now. And ἅμα which alone means together (or: at the same time), and with a noun means [together] with, and requires dative case forms.
 

1. Accentuation:
   question words (interrogatives) versus indefinite adjectives and pronouns.
   What's the meaning of ποῦ? and of που?
   Which of the following means Where to? ποι or ποῖ?
   Which of the following means When? πότε or ποτέ?
2. If together with his father is: ἅμα τῷ πατρί (ὁ πατήρ, τοῦ πατρός)
   What is: together with his mother? (ἡ μήτηρ, τῆς μητρός)
   And: he runs with his dog. (ὁ κύων, τοῦ κυνός)
   And: He dines together with his child.