Someone please make sense of the part where it starts from “example, consider f(5) +3:
f(5)+3=52 - 7+3=25-7+3=21”
My question is how did this come to being.

Part a: sam rented a boat at $225 for 2 days. if he rents the same boat for 5 days, he has to pay a total rent of $480. write an equation in the standard form to represent the total rent (y) that sam has to pay for renting the boat for x days. (4 points)