Could really use some help with this quiz hurry please I really need the help

Explain how you can use the associative property to evaluate (7x50)x4.

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)

Anyone? 15m is what percent of 60m; 3m; 30m; 1.5 km?