в) $$ \frac{2a}{a^2-9} - \frac{1}{a+3} = \frac{2a}{(a-3)(a+3)} - \frac{1}{a+3} = \frac{2a - (a-3)}{(a-3)(a+3)} = \frac{2a - a + 3}{(a-3)(a+3)} = \frac{a+3}{(a-3)(a+3)} = \frac{1}{a-3} $$
Ответ: $$ \frac{1}{a-3} $$