Answer :

iGreen
5/6 and -3/8

Denominators: 6 and 8

We want a the smallest number 6 and 8 can get into.

6:

6, 12, 18, 24, 30, 36, 42, 48

8:

8, 16, 24, 32, 40, 48, 56, 64

As you can see, the smallest number that both 8 and 6 can get into is 24.