б) 6a x-2y

б) Выполним сложение дробей:

$$\frac{6a}{x-2y} + \frac{2a}{x+y} = \frac{6a(x+y)}{(x-2y)(x+y)} + \frac{2a(x-2y)}{(x-2y)(x+y)} = \frac{6ax + 6ay + 2ax - 4ay}{(x-2y)(x+y)} = \frac{8ax + 2ay}{(x-2y)(x+y)} = \frac{2a(4x+y)}{(x-2y)(x+y)} = \frac{2a(4x+y)}{x^2 + xy - 2xy - 2y^2} = \frac{2a(4x+y)}{x^2 - xy - 2y^2}.$$

Ответ: $$\frac{2a(4x+y)}{x^2 - xy - 2y^2}$$