Verified answer

This is a limiting reagent problem.

That means you have to do the calculation for both reactants and pick the one that gives the smallest amount of product.

39.6 g C6H6 * ( 1 mol)/ xxx.x g C6H6) * (12 mol CO2/2 mol C6H6) * ( 44.01 g/mol CO2) = g CO2

You will have to calculate the molecular wt of C6H6 for xxx.x

133.8 g O2 * ( 1 mol)/ 32.00 g O2) * (12 mol CO2/15 mol O2) * ( 44.01 g/mol CO2) = g CO2

So do the math on both of these and see which equation produces the least amount of CO2.