a) $$ \frac{ax + bx - ay - by}{bx - by} = \frac{x(a + b) - y(a + b)}{b(x - y)} = \frac{(a + b)(x - y)}{b(x - y)} = \frac{a + b}{b} $$
Ответ: $$\frac{a+b}{b}$$