What is the length, in units, of the hypotenuse of a right triangle if each of the two legs is 3 units? square root of 18 units square root of 27 units 3 units 6 units

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! )