To solve this, we must know some terms:
% Yield = (Actual yield / Theoretical yield) x 100
Actual yield is already given = 7.64 moles
To obtain the theoretical yield, we use stoichiometry and proceed like this:
C3H8 + 5O2 => 3CO2 + 4H2O
1 mole C3H8 ------- 3 x 1 mole CO2
4.5 moles C3H8 ------ x
x = 13.5 moles
Therefore, our % yield:
% Yield = (7.64 moles/13.5 moles) x 100 = 57 % approximately
Answer: % yield = 57 %