Please help me with this question, I only need help with c), I already know the others, a) 9pi metres squared, b) 8pi metres squared, and d) 54.5metres squared.

Charlie is at an amusement park that has 18 different rides. each ride costs $1.75. the function c(r) = 1.75r represents the total amount of money that charlie will spend if he goes on r rides, but he never goes on the same one more than once. what domain and range are reasonable for the function?