The equations means that four moles of CH3NO2 reacts with three moles of oxygen to yield for moles of carbon dioxide, two moles of nitrogen gas and six moles of water.
The balanced equation of the reaction is;
4CH3NO2 + 3O2 -----> 4CO2 + 2N2 + 6H2O
Molar mass of CH3NO2 = 61 g/mol
61 g of methyl nitrate contains 61 g/ 61 g/mol = 1 mole of CH3NO2
From the balanced reaction equation;
4 moles of CH3NO2 reacts with 3 moles of oxygen
1 mole of moles of CH3NO2 reacts with 1 * 3/4 = 0.75 moles of oxygen gas
0.75 moles of oxygen gas * 32 g/mol = 24 g of oxygen
