A school has 20 classrooms. One
fourth of the classrooms are
for kindergarten and first
grade. Twice as many are
for second and third grade.
The rest are for fourth and
fifth grade. What percent
of the classrooms are for 45
or 5th graders

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! )