RETAIL The sales department for a clothing store is planning to change the
price of their most popular sport jacket line. The current price of each jacket
is $75, and last year 81 jackets were sold. The sales department estimates
that every increase of $5 would result in a decrease in sales of 3 jackets.

a. Define variables and write a function to represent the situation.

b. How much should each jacket cost to maximize the revenue from sales?

c. Find the domain and range in the context of this situation.