Familia Romana - pensa

Salvete Omnes!
If anyone could point out the mistakes in the following from Pensum C it would be really appreciated.

Capitulum IV
Quot nummi sunt in sacculo Iulii? Decem nummi sunt in sacculo Iulii
Adestne Davus in scaena prima? Davus in scaena prima non adest
Quis Davum vocat? Davum dominus vocat
Suntne nummi Iulii in sacculo Davi? Nummi Iulii non in sacculo Davi sunt
Quid Iulius ponit in sacculo Davi? Iulius ponit in sacculo Davi, quia Davus est probus servus*
Quot nummi iam in sacculo Iulii sunt? Novem nummi iam in sacculo Iulii sunt
Estne vacuus sacculus Medi? Sacculus Medi non vacuus
Cur Medus discedit? Medus discedit, quia pecuniam Iulii is habet**
Quem Iulius vocat? Iulius Medum vocat
Cur Medus Iulium non audit? Medus Iulium non audit quia is abest

Extract from Pensum B
Sacculus Davi vaccus est, in sacculo ____ nulla pecunia est.
Apparently eius is the correct answer not suo. I assume that is because if ‘suo’ was used it would refer to the bag, and the sentence would not make sense. If this is true ‘suus, -a, -um’ is used mostly with the nominative case?

*Quid can mean why/what - both make sense in the given context, which one should be assumed?
**Is the ‘is’ neccessary?

Thanks for your help

A minor point: I would write

Dominus Davum vocat
because it puts emphasis on dominus. If the question had been Quem dominus vocat? Then my answer would have been Davum dominus vocat, as you wrote.

Suus can be in any case: Davus habet saccum suum. Davus oblitus est sacci sui. You get the gist.

In your example quid most likely means “what” rather than “why”, since pono is a transitive verb and we assume that there is an object we put somewhere.
Quid Iulius pecuniam ponit in sacculo Davi? In this case it must mean why.

is doesn’t seem to be necessary.

Sorry, I meant if suus, -a, -um had to refer to “a subject which is in the nominative case”: which would explain why it refers to pecunia (nom) not Iulii (gen)

Also, would the below correction be correct?
Iulius unum nummum ponit in sacculo Davi

Gratias tibi ago

*sacculus (nom), Davi (gen)

  1. No, it doesn’t have to. For example, the subject of a infinitive + accusative sentence is, of course, in the accusative. And if you a have a participle, all cases are virtually possible.

  2. It looks OK to me.

Vale!