Sean drove at a faster rate because if you divide each miles/minutes then it gives you how many miles per minute they drive. 20/5 is 4, and 45/9 is 5, and 5 is greater than 4.
A = p = principal amount (the initial amount you borrow or deposit) r = annual rate of interest (as a decimal) t = number of years the amount is deposited or borrowed for. A = amount of money accumulated after n years, including interest. n = number of times the interest is compounded per year