balance equation is given as
2 C₄H₁₀+ 13 O₂ = 10 H₂ O + 8 CO₂
since 6 mol of butane is burns , we multiply both side by "3" as 3 x 2 = 6
multiplying each term by "3"
(3 x 2) C₄H₁₀+ (13 x 3) O₂ = (10 x 3) H₂ O + (8 x 3) CO₂
6 C₄H₁₀ + 39 O₂ = 30 H₂ O + 24 CO₂
from the equation , we see that when 6 moles of butane are burnt , we get 24 moles of carbon dioxide