Add :

5a + 3b, a - 2b, 3a + 5b

5a + 3b + a - 2b + 3a + 5b

Arrange the polynomial with like terms together and combine them.

= (5a + a + 3a) + (3b - 2b + 5b)

= 9a + 6b

Hence, addition of 5a + 3b, a - 2b, 3a + 5b is 9a + 6b.