monthly sales. HINT [See Example 4(a).] The monthly sales of Sunny Electronics' new sound system are given by q(t) = 4,000t - 100t units per month, t months after its introduction. The price Sunny charges is p(t) = 2,000 - t dollars per sound system, t months after introduction. Find the rate of change of 9' (t ) = Find the rate of change of the price. p'(t ) = Find the rate of change of monthly revenue 5 months after the introduction of the sound system. $ per month Interpret your answer. When t = the revenue is increasing at a rate of $ per month