з) $$10ax + 5bx - 5x + 10ay + 5by - 5y = 5(2ax + bx - x + 2ay + by - y) = 5(x(2a + b - 1) + y(2a + b - 1)) = 5(2a + b - 1)(x + y)$$
Ответ: $$5(2a + b - 1)(x + y)$$