How do i change an equation to equal y or equal x?

Adam used 1072.4 gallons of water over the course of 7 days. how much water did adam use, on average, each day?

Pls never taught i’m really confused and i rlly need

At your job you're paid $50 per week plus $3 per sale at least how many saled do you need to make in order to have over $250