To solve the first equation:
(5/21 + 2/15) + 2/21

First, find a common denominator for 21 and 15, which is 105.

(25/105 + 14/105) + 10/105
39/105 + 10/105
49/105 = 7/15

Therefore, (5/21 + 2/15) + 2/21 = 7/15

To solve the second equation:
(2/35 + 3/28) + 1/28

First, find a common denominator for 35 and 28, which is 140.

(8/140 + 15/140) + 5/140
23/140 + 5/140
28/140 = 1/5

Therefore, (2/35 + 3/28) + 1/28 = 1/5