Given total cost TC=3q² + 7q + 12. Evaluate the marginal cost and average cost if q=3.

Total Cost TC=3q² + 7q + 12

q=3 (Given)

Marginal cost:

TC/q=3*2q +7+0

=6q+7

Since q=3,

6q+7 =6*3 +7

= 18 + 7

= 25

Marginal cost if q=3 is 25.

Average cost:

Average cost= TC/q

And q = 3,

Average Cost = (3*3² + 7*3 + 12)/3

= (27+21+12)/3

= 60/3

= 20

Average cost if q=3 is 20.