Okay, the two values you've got is 2 2/3 and 1 1/4.
Convert both of those values into improper fractions, which is 2 2/3 = 8/3 and
1 1/4 = 5/4
Now, subtract those two values: 8/3 - 5/4, find the lowest common denominator, which is 34 = 12...
8/3 - 5/4 = (84 - 5*3)/12 = (32 - 15)/12 = 17/12 = 1 5/12
