A box contains 5 red balls and 8 white balls. In how many ways can we choose 6 balls, 3 of which are white?

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?