To calculate each of these expressions, we need to find a common denominator first.

1) 2/7 + 3/5
Common denominator = 35
(2/7) (5/5) = 10/35
(3/5) (7/7) = 21/35
Adding these together, we get:
10/35 + 21/35 = 31/35

2) 3/4 - 3/5
Common denominator = 20
(3/4) (5/5) = 15/20
(3/5) (4/4) = 12/20
Subtracting these, we get:
15/20 - 12/20 = 3/20

3) 1/3 + 1/6
Common denominator = 6
(1/3) * (2/2) = 2/6
(1/6) = 1/6
Adding these together, we get:
2/6 + 1/6 = 3/6 = 1/2

Therefore, the results of the expressions are:
1) 2/7 + 3/5 = 31/35
2) 3/4 - 3/5 = 3/20
3) 1/3 + 1/6 = 1/2