9/4 - 1
make 1 into a fraction
9/4 - 1/1
then make them have common denominator
9/4 - 1/1 multiply 1/1 by 4/4 (which simplified will be one so you're not messing it up)
9/4 - 4/4 now subtract the 4/4 out of 9/4
(you don't subtract the denominators)
so 9 - 4 is 5
9/4 - 4/4 = 5/4
Hope this helps:)