Help with this!!

Show steps pls :)

Select all the expressions that will include a remainder.

How do you determine if an ordered pair is a solution to a given equation?

I'm at a bookstore with $\$35$ in my pocket and a $20\%$-off coupon. what is the cost of the most expensive book i can buy with my money and the coupon? (assume that there are books of every possible price in the bookstore. it's a large bookstore! )