First: You need to make the denominator(bottom number) of the fractions equal to each other. You do this by finding a number that they are both divisible by. One of the easier ways in this example would be to multiply the bottom number together, 3 x 4 = 12.
Second: In order to have the fraction still be equivalent but with a denominator that is 12. You would have to multiple the top and bottom numbers (5/4) by 3 and the top and bottom numbers of (1/3) by 4.
5/4 is the same as 15/12
1/3 is the same as 4/12
Now you can subtract the top numbers 15/12 - 4/12 = 11/12
