4) 2a+5b - 2a-3b; ab ab

4) $$\frac{2a+5b}{ab} - \frac{2a-3b}{ab} = \frac{2a + 5b - (2a - 3b)}{ab} = \frac{2a + 5b - 2a + 3b}{ab} = \frac{8b}{ab} = \frac{8}{a}$$

Ответ: $$\frac{8}{a}$$