If 7.79 mol of NO2 occupy 17.8 L, how many liters will 4.31 mol of NO2 occupy at the same temperature and pressure?

Can someone me with questions 12 and 13 plz.

How many liters of oxygen gas, at standard temperature and pressure, will react with 35.8 grams of iron metal? 4 fe (s) + 3 o₂ (g) → 2 fe₂o₃ (s)

The number to the right of an element's symbol (ex. c-12) identifies the of an isotope.