13) $$\frac{5x-2y}{a} - \frac{3x+y}{a} = \frac{5x-2y - (3x+y)}{a} = \frac{5x-2y - 3x - y}{a} = \frac{2x - 3y}{a}$$
Ответ: $$\frac{2x-3y}{a}$$