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: $$\frac{a+b}{b}$$