3.) Calculate the mass of oxygen gas that can be produced in the decomposition of 5.55 g of silver oxide.

This is what I did but is it right?... I need help with a few more btw to double check if i'm doing these right.

So here is what I did:
First: balance the equation
2 Ag2 O decomposes→ 4 Ag + O2

So, (btw I put parenthesis to make it visibly understandable if it helps)
5.55 g Ag2O * (1 mole Ag2O/ 139.868 g Ag2O) * (1 mol O2/ 1 mol Ag2O) * (31.998 g O2/ 1 mole O2) = 1.27 g O2.... since the ? is asking to calculate the mass of Oxygen gas (O2)

1.) what mass of zinc is needed to completely react with 4.00 g of silver nitrate?

2.) If excess ammonium sulfate reacts with 22.5 g of calcium hydroxide according to the following unbalanced chemical equation:
(NH4)2 SO4 + Ca (OH)2 → CaSO4 + NH3 + H2O
So,