Need help in calculating this problem. Can you please help me solve it?

Demand for Tablet Computers The quantity demanded per month, x, of a certain make of tablet computer is related to the average unit price, p (in dollars), of tablet computers by the equation x = f(P) = - 100 9 810,000 - pz It is estimated that t months from now, the average price of a tablet computer will be given by 400 P(t) = + 200 (0 s t = 60) dollars. Find the rate at which the quantity demanded per month of the tablet computers will be changing 36 months from now. (Round your answer to one decimal place.) 11.8 * tablet computers/month