$$\frac{6x}{x^2 - 16} + \frac{24}{x^2 - 16} = \frac{6x+24}{x^2-16} = \frac{6(x+4)}{(x-4)(x+4)} = \frac{6}{x-4}$$
Ответ: $$\frac{6}{x-4}$$