To add 3/5 + 2/7, we need to find a common denominator. The least common denominator for 5 and 7 is 35.

3/5 7/7 = 21/35
2/7 5/5 = 10/35

Now we can add them together:

21/35 + 10/35 = 31/35

Next, to subtract 11/15 - 3/5, we need to find a common denominator. The least common denominator for 15 and 5 is 15.

11/15 - 9/15 = 2/15

Lastly, to subtract 5/6 - 1/4, we need to find a common denominator. The least common denominator for 6 and 4 is 12.

5/6 2/2 = 10/12
1/4 3/3 = 3/12

Now we can subtract them:

10/12 - 3/12 = 7/12

Therefore, the results are:

3/5 + 2/7 = 31/35
11/15 - 3/5 = 2/15
5/6 - 1/4 = 7/12