Before he went to the hairdresser, Shel's hair was 71/4 inches long. When he left the salon, it was 51/2 inches long. How much of his hair did Shel get cut off?

Do you understand the idea of the problem, that it's simple subtraction?
It seems a shame to just give the answer.
One way to do fractions quickly is to change one of them to the other, such as 7 1/2 - 5 1/2, then deal with the difference between 1/4 and 1/2, easy, just lop off 1/4 from your answer.