Priya is stacking blocks to make a tower .Dhe takes a break when the tower is 2 1/2 feet tall wich is 5/8 of the height of the tower she wants to build . How tall is the tower when she fenished ?

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! )