super urgent! not sure about the answer for c too

A local sandwich shop faces the following costs of production per hour depending on how many sandwiches it makes. Sandwiches per hour Total cost $9 $10 $12 3 $15 4 $20 $27 6 $36 7 $49 8 $64 [For parts a. and b. below, enter the correct numerical answer in the answer space.] a. If the shop produces seven sandwiches per hour, then its average cost is b. The marginal cost for the seventh sandwich is c. Suppose the market for sandwiches is perfectly competitive, and the market price for a sandwich is $8. The shop will maximise its profits if it sells 3 + sandwiches