Janet invested $10,000, part at 2% and part at 12%. if the total interest at the end of the year is $600, how much did she invested at 2%

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?