Example 3 - Maximize Revenue

Alex runs a snowboard rental business that charges $12 per snowboard and averages 36 rentals per day. She discovers that for each $0.50 decrease in price, her business rents out two additional snowboards per day.
a) What is the maximum revenue?
b) What does the x of the vertex represent?
c) At what price can Alex maximize her revenue?
d) How many snowboards must be sold to maximize her revenue?