I had to answer a question similar to that one on Math XL. This question was about renting a truck instead of needing a 48 mile taxi. (Took me a long time just to find the truck question, but I am giving you the truck help me answer the question, in hopes that it will help you.)
The cost of renting a truck from Hamilton Auto Rental is $47.60 per day plus $0.15 per mile. The expression 47.60 plus 0.15 m represents the cost of renting a truck for one day and driving it m miles. Evaluate 47.60 plus 0.15 m for m equals 120.
Substitute the numerical value for each variable into the expression and simplify the result.
I am sorry if that didn't help you, but it was the closest thing I could find to use to help you.