Maxon spent 15 hours doing her homework last week this week she spent 18 hours doing homework she says that she spent 120% more time doing homework this week is she correct show your work to justify your decision

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! )