Choose the most appropriate unit to measure each. write mm, cm, dm, m, or km. which one would you use to measure the distance between paris and london?

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! )