precal
posted by Anonymous .
Spider Industries is a U.S.based company that testmarketed an electronic cobweb destroyer in Japan. The company's revenue, R, is a function of the number of destroyers sold, x, using the following formula R = 160x 0.2x^2.
How many destroyers must the company sell to maximize its revenue?
75, 400, or 40.

At maximum revenue, dR/dx = 0
That means 160  0.4x = 0
Solve for x.