Molar mass:
CH₄ = 12 + 1 x 4 = 16.0 g/mol
CO₂ = 12 + 16 x 2 = 44.0 g/mol
Balanced equation :
CH₄ + 2 O₂ = CO₂ + 2 H₂O
16.0 g CH₄ --------------- 44.0 g CO₂
(mass of CH₄) ----------- 46.4 g CO₂
mass of CH₄ = 46.4 x 16.0 / 44.0
mass of CH₄ = 742.4 / 44.0
= 16.87 g CH₄
hope this helps!