a: \(=\left(\dfrac{-2}{x-2}+\dfrac{1}{x+2}-\dfrac{x-3}{\left(x-2\right)\left(x+2\right)}\right)\cdot\dfrac{-\left(x-2\right)\left(x+2\right)}{4x-6}\)
\(=\dfrac{-2x-4+x-2-x+3}{\left(x-2\right)\left(x+2\right)}\cdot\dfrac{-\left(x-2\right)\left(x+2\right)}{4x-6}\)
\(=\dfrac{-2x-3}{2\left(2x-3\right)}\cdot\left(-1\right)=\dfrac{2x+3}{2\left(2x-3\right)}\)
b: \(=\dfrac{5x-15-3x-9+x+24}{\left(x-3\right)\left(x+3\right)}\cdot\dfrac{-\left(x-3\right)\left(x+3\right)}{2x\left(x+2\right)}\)
\(=\dfrac{3x}{-2x\left(x+2\right)}=\dfrac{-3}{2\left(x+2\right)}\)