Product Rule Word Problem

[Dazed]

A music store has determined that the number od CDs sold monthly is

Number = 6250(.9286^x) Cds where x is the price in dollars.

1. Give an equation for revenue as a function of price.

2. If each CD costs the store $7.50, find an equation for profit as a function of price.

3. Find the formula for the rates of change of revenue and profit.

I don't understand how to find the equations for revenue and profit. I know profit = revenue - total cost. The total cost would be the formula given right?

 

[Gene]

Number = 6250(.9286^x) Cds where x is the price in dollars.

1. Revenue = number times price.
R = Nx = 6250x(.9286^x)

2. Profit = revenue - cost
P = 6250x(.9286^x)-7.50x