Please answer please, I got 300,000 for c.

14. The monthly sales of Sunny Electronics' new stereo system are given by S(x) = 30x - x2 hundred units per month, x months after its introduction. The price Sunny charges is p(x) = 800 - x2 dollars per stereo system, x months after its introduction. The revenue Sunny earns then must be R(x) = 100p(x)S(x) a. Write the revenue function in explicit form as a function of x4 b. Marginal revenue function c. Find the rate of change of revenue 10 months after introduction