The total cost (in dollars) of producing $x$ coffee machines is $$C(x) = 1700 + 50 x - 0.2 x^2.$$
(A) Find the exact cost of producing the 21st machine.
Exact cost of 21st machine =
(B) Use marginal cost to approximate the cost of producing the 21st machine.
Approx. cost of 21st machine =