The monthly revenue R achieved by selling x wristwatches is figured to be R(x)=85x-0.2x^2. The monthly cost C of selling x wristwatches is C(x)=32x+1850.

A. How many wristwatches must the firm sell to maximize revenue? What is the maximum revenue?

B. Profit is given as P(x)=R(x)-C(x). What is the profit function?

C. How many wristwatches must the firm sell to maximize profit? What is the maximum profit?

For the quadratic function ax^2 + bx + c where a<0 the point of maximum is x0=-b/(2a).

A) here a = -0.2, b = 85, x0 = -b/(2a) = 85/0.4 = 212.5. Because the number of wristwatches must be integer, there are two possibilities: 212 and 213. For both variants R(x)=9031.2 (R(212.5) = 9031.25).