Решение:

1. $$\frac{5b}{28} + \frac{9b}{28} = \frac{5b+9b}{28} = \frac{14b}{28} = \frac{b}{2}$$

   Ответ: $$\frac{b}{2}$$

2. $$\frac{9m}{7n} - \frac{2m}{7n} = \frac{9m-2m}{7n} = \frac{7m}{7n} = \frac{m}{n}$$

   Ответ: $$\frac{m}{n}$$

3. $$\frac{5x-3y}{8z} + \frac{3x-13y}{8z} = \frac{5x-3y+3x-13y}{8z} = \frac{8x-16y}{8z} = \frac{8(x-2y)}{8z} = \frac{x-2y}{z}$$

   Ответ: $$\frac{x-2y}{z}$$

4. $$\frac{4c-3d}{cd} - \frac{c-3d}{cd} = \frac{4c-3d-(c-3d)}{cd} = \frac{4c-3d-c+3d}{cd} = \frac{3c}{cd} = \frac{3}{d}$$

   Ответ: $$\frac{3}{d}$$

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

   Ответ: $$\frac{6}{x+4}$$

2. Упростите выражение:

1. $$\frac{a-2}{a-1} - \frac{a}{1-a} = \frac{a-2}{a-1} + \frac{a}{a-1} = \frac{a-2+a}{a-1} = \frac{2a-2}{a-1} = \frac{2(a-1)}{a-1} = 2$$

   Ответ: $$2$$

2. $$\frac{3y+7}{4-y} + \frac{y+15}{y-4} = -\frac{3y+7}{y-4} + \frac{y+15}{y-4} = \frac{-3y-7+y+15}{y-4} = \frac{-2y+8}{y-4} = \frac{-2(y-4)}{y-4} = -2$$

   Ответ: $$-2$$