X over 21 equals 12/18

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?

What classification best describes 5x+10y+15z=60 2x+4y+6z=60 x+2y+3z=60

How do you solve this equation 26x=74