In order to subtract one fraction from another fraction, you will need to find the lowest common denominator. The lowest common denominator is the smallest number that can be exactly divided (meaning no remainders) by all of the bottom numbers in a set of fractions. In this case, we need to find the lowest common denominator for 4 and 5. An easy trick is to multiply those 2 numbers together, but then you still have to double check that there isn't a lower number that is also divisible by both of them.
In this case, 4x5=20, and there aren't any lower shared multiples (For 4: 4, 8, 12, 16, 20; for 5: 5, 10, 15, 20).
At this point, it's also easier to make the whole number a fraction. To do that, you multiply 9 by 4 then add one: 9x4+1=37. So that one is 37/4. Using the same process, 4x5+3=23, so that fraction is 23/5.
Now, we'll use our lowest common denominator of 20. For 37/4, you have to multiply both top and bottom by 5 (since 4x5=20). That gives you 185/20. For 23/5, you have to multiply both top and bottom by 4. That gives you 92/20.
Now you have a much simpler problem! 185/20 - 92/20. The denominator stays the same, so you subtract 185-92 and get 93/20. Now you'll want to reduce that fraction. There are 4 sets of 20 in 93, with 13 leftover. So that gives us 4 13/20.