Formula for this please

Question

If 16.8 L of carbon dioxide gas is produced at STP in the following reaction, how many grams of methane (CH4) were burned?

Answer 1

Combustion of methane:

CH₄ + 2O₂ ==> CO₂ + 2H₂O

At STP 1 mol of ideal gas = 22.4 L

16.8 L x 1 mol/22.4 L = 0.75 Moles CO₂

0.75 mol CO₂ x 1 mol CH₄/mol CO₂ x 16 g/mol CH₄ = 12 g CH₄