Odpowiedź:
1.
5(x + 3y) + 6(2x + y) = 5x + 15y + 12x + 6y = 17x + 21y
2.
2(3a + b) - (4a + b) = 6a + 2b - 4a - b = 2a + b
3.
-3(x-2y) - (4x - 9y) = -3x + 6y - 4x + 9y = -7x + 15y
