Can someone check if my answer for this quick math problem?

Question

A concert promoter estimates that if he sells tickets at a price of $15 each, he will sell 200 tickets. For each dollar that he decreases the price he will sell 20 more tickets. Express the total revenue R from ticket sales as a function of the ticket price p. Graph the result and estimate the optimum ticket price.

My ANSWER:

x,y
15, 200

slope= -20

200= -20(15)+b

200+300=b
b=500

Equation for price: (p) -20x+500

Equation for Revenue: ???

How do you write the Revenue function as a function of the ticket price p?

Answer 1

You actually have a function for ticket sales:

s = -20p + 500
when p = 15, s = 200

R = s * p = -20p squared + 500p