If you have 20 coins worth $1.35, and you only have nickels and dimes, how many do you have of each coin?

N + d = 20n = 20 - d
0.05n + 0.10d = 1.35

0.05(20 - d) + 0.10n = 1.35
1 - 0.05d + 0.10d = 1.35
-0.05d + 0.10d = 1.35 - 1
0.05d = 0.35
d = 0.35/0.05
d = 7 < 7 dimes

n + d = 20
n + 7 = 20
n = 20 - 7
n = 13 <=== 13 nickels

The answer is 225 miles per 4.5 hours. hope this ; )