Combine like terms to write an equivalent expression. Then use y = 5 to prove the expressions are equivalent.

1 + y + y + y + 1

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! )