a. The change after 1 hour is 2 inches because 6x10=60 (minutes) and you multiply 1/3 by 6/1 and get 6/3 or 2 inches.
b. The change after 2.25 hours is 4 1/2 inches because 2x2=4 and .25 (1/4) of an hour is 15 minutes so take 1/3 and multiply it by 1/2 (half of 10 is 5 and 10+5=15 min.) and you get 1/6 and then you add 1/3 and 1/6 together to get 1/2. So together it is 4 1/2 inches.