The sum of half a number and four

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 else equals 42 and 30 for multiply

Can someone me and explain..will award brainlest!