calculus application

Question

A company's revenue from selling  units of an item is given as

𝑅(𝑥)=1000𝑥−𝑥^2 (dollars).

If sales are increasing at the rate of 8 units per day, find how rapidly the revenue is growing (in dollars per day) when  units have been sold?

Answer 1

dx/dt = 8

X = 400

R(x) = 1000x – x²

R’(x) = (1000-2x) (dx/dt)

=[1000-2(400)] * 8

=200 * 8

=1600 dollars/day