To add these fractions, we need to find a common denominator.

The least common multiple of 15, 21 is 105.

So, we rewrite the fractions with a common denominator of 105:

(5/21) (5/5) = 25/105
(2/15) (7/7) = 14/105
(2/21)

Now, we add the fractions together:

25/105 + 14/105 + 2/21

= 41/105 + 2/21

To add these two fractions, we need to find a common denominator.

The least common multiple of 21, 105 is 105.

So, we rewrite the fractions with a common denominator of 105:

(41/105) + (10/105)

Now, we can add the fractions together:

41/105 + 10/105
= 51/105

Therefore, the result is 51/105.