math question

Question

A store has been selling 1000 television sets a week at $450 each. A market survey indicates that for each $10 rebate offered to buyers, the number of sets sold will increase by 100 per week.

a) Find the demand function

b) How large a rebate should the company offer buyers in order to maximize its revenue?

Answer 1

R(r) = (1000 + 100r)(450 - 10r), r represents the number of rebates

Convert to vertex form and answer?