4) \frac{5x-10}{x^{2}+14x+49} \cdot \frac{4x+28}{x-2}.

4) $$\frac{5x-10}{x^{2}+14x+49} \cdot \frac{4x+28}{x-2} = \frac{5(x-2)}{(x+7)^{2}} \cdot \frac{4(x+7)}{x-2}=\frac{5 \cdot 4}{x+7}=\frac{20}{x+7}$$

Ответ: $$\frac{20}{x+7}$$