At Bert's Bootery, the Total Cost of Producing Twenty Pairs

Multiple Choice

At Bert's Bootery, the total cost of producing twenty pairs of boots is $400. The marginal cost of producing the twenty-first pair of boots is $83. We can conclude that the

A) average variable cost of 21 pairs of boots is $23.
B) average total cost of 21 pairs of boots is $23.
C) average total cost of 21 pairs of boots is $15.09.
D) marginal cost of the 20th pair of boots is $20.