The monthly sales of Sunny Electronics' new sound system are given by q(t) - 4,000c - 60² units per month, t months after its introduction. The price Sunny charges is p(t)- 2,000 - ² dollars per

sound system, t months after introduction. Find the rate of change of monthly sales. HINT [See Example 4(a).]

q'(1) -

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.