Ответ:

(a+b)×5 + 9a + 3b = 5a + 5b + 9a + 3b = 14a + 8b.

13×(a+b) - 7b + 4a = 13a + 13b - 7b + 4a = 17a + 6b

6 × (x + a) - 5a = 6x + 6a - 5a = 6x + a

30x - (5x + 4x) = 30x - 9x = 21x