Using the information from the table below, answer the following questions.

Production ⇔ Total cost
0 ⇔ 80
1 ⇔ 140
2 ⇔ 180
3 ⇔ 200
4 ⇔ 240
5 ⇔ 320
6 ⇔ 420
7 ⇔ 540
8 ⇔ 680

a. Total average costs for the production of 4 products.
b. Marginal cost for the production of the 6th product.
c. If its price is 100$, find the maximum profit for a perfectly competitive firm (MR=MC).