5x - 5y + x + y = 5(x - y) + (x + y) = 5(x - y) + 1(x + y) = (5x - 5y) + (x + y) = 5(x - y) + 1(x + y) = 5(x - y) + 1(x + y) = (5 + 1)(x - y) = 6(x - y)