15) (b+2)/(b²-9) - b/(9-b²) =

Преобразуем выражение:

$$\frac{b+2}{b^2 - 9} - \frac{b}{9 - b^2} = \frac{b+2}{b^2 - 9} + \frac{b}{b^2 - 9} = \frac{b+2+b}{b^2-9} = \frac{2b+2}{b^2-9} = \frac{2(b+1)}{(b-3)(b+3)}$$

Ответ: $$\frac{2(b+1)}{(b-3)(b+3)}$$