On his twelfth birthday ben was 4 3/4 feet tall on his thirteen birthday ben was 5 3/8 feet tall. how much did ben grow beetween his twelfth and thirteen birthdays

So, to get the answer you have to subtract the old height to the new one..
First, 4 3/4 = 19/4 because we have to get a fraction, rather than a mixed number. 4x4=19+3= 19/4
 
Now, changing the other mixed number, 5 3/8 . 5x8=40+3= 43/8

We have to get both denominators(the bottom half of the fraction) to be the same.
19/4 and 43/8, 19/4 the denominator is 4 and if you times it by 2 you'd get 8 which would be the same denominator as the other fraction.

What ever you do to the top you do to the bottom, so you time 19 as well.
So, now 19/4 becomes 38/8 and now we subtract.
38/8-43/8= -5

There you go..