The total revenue (in dollars) from the sale $x$ coffee machines is $$R(x) = 2500 + 70 x - 1 x^2.$$
(A) Find the exact revenue from the sale of the 21st machine.
Exact revenue from the sale of the 21st machine =
(B) Use marginal revenue to approximate the revenue from the sale of the 21st machine.
Approx. revenue from the sale of the 21st machine =

(Round answers to three decimal places as needed.)

Hint: