Output Average Fixed Cost Average Variable Cost 1 $50.00 $100.00 2 25.00 80.00 3 16.67 66.67 4 12.50 65.00 5 10.00 68.00 6 8.37 73.33 7 7.14 80.00 8 6.25 87.50 The marginal cost of the fifth unit of output is:__________ a. $62. b. $78. c. $3. d. $80.