A student club is planning a fundraising car wash. last year they

A student club is planning a fundraising car wash. Last year they charged $10 per vehicle and washed 120 vehicles. They would like to earn more money this year. For every $1 increase in price, they know they will wash 5 fewer vehicles. 
a) Write a quadratic function to model this situation using v as the number of vehicles and r as the revenue.
b) Determine the best price to charge for the car wash and the revenue expected at that price. 
ps. (use completing the square where necessary.)