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6-23.

An electronics store purchases stereos from a supply company at a cost of $63 each. They currently sell the stereos for $99. At this price, the store is averaging 23 sales per week. Marketing studies show that for every $2 decrease in price, the store will sell an additional 5 stereos. What price should the store use to maximize their profits? Homework Help ✎

Revenue = (profit)(number sold)

Calculate the current revenue:
Profit: $99 - $63
Number sold: 23

Adjust the current revenue equation:
Let x = the number of times the price is decreased by $2.

R(x) = (36 − 2x)(23 + 5x)

Optimize (that is, use derivatives to find the optimal value of x). But note, the question is asking about price, not x.