Note that when you subtract a negative number it changes it to adding a positive number.
5/6 - (-3/4) → 5/6 + 3/4
Now, lets find common denominators.
5/6 = 10/12
3/4 = 9/12
Add.
10/12 + 9/12 = 19/12
This cannot be simplified any further.
Best of Luck!