a) $$ \frac{3-2a}{2a} - \frac{1-a^2}{a^2} = \frac{(3-2a)*a - (1-a^2)*2}{2a^2} = \frac{3a-2a^2 - 2 + 2a^2}{2a^2} = \frac{3a-2}{2a^2} $$.
б) $$ \frac{1}{3x+y} - \frac{1}{3x-y} = \frac{3x-y - (3x+y)}{(3x+y)(3x-y)} = \frac{3x-y-3x-y}{9x^2 - y^2} = \frac{-2y}{9x^2 - y^2} $$.
Ответ: a) $$ \frac{3a-2}{2a^2} $$; б) $$ \frac{-2y}{9x^2 - y^2} $$