Answer
91 %
Work Step by Step
Percent yield is found by dividing the actual yield by the theoretical yield. In this case, the actual yield was 39 miles per gallon and the theoretical yield was 43 miles per gallon. Calculate by dividing the two values:
39 $\div$ 43 $\approx$ 0.906
0.906 x 100 = 90.6 %
Round up to 91 %.