Hey there!
First, we need to bring 7/8 and 1/3 to have the same denominator (we do this so we will be able to subtract easier).
To do that all you will need find a number, both 3 and 8 go into, or multiply them, (the closest to those numbers), this would be 24. The work is shown below:
7/8 times 3/3 is 21/24
1/3 times 8/8 is 8/24
Therefore this is the same equation.
Solve.
21/24 - 8/24 = 13/24
This cannot be simplified.
So, your answer is 13/24.
Hope this helps, and sorry if I was confusing!