With some species of bamboo, you can actually see them grow. You could observe 30 centimeters of growth in just 1/3

of a day. At what rate does this bamboo grow?

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! )