#### Problem 76E

76. The cost, in dollars, of producing $x$ units of a certain commodity is

$C(x)=920+2 x-0.02 x^{2}+0.00007 x^{3}$

(a) Find the marginal cost function.

(b) Find $C^{\prime}(100)$ and explain its meaning.

(c) Compare $C^{\prime}(100)$ with the cost of producing the 101st item