\(P=\left(\dfrac{2x}{x+3}+\dfrac{x}{x-3}-\dfrac{3x^2+3}{x^2-9}\right):\left(\dfrac{2x-2}{x-3}-1\right)\)
\(\Rightarrow P=\dfrac{2x\left(x-3\right)+x\left(x+3\right)-\left(3x^2+3\right)}{\left(x+3\right)\left(x-3\right)}:\dfrac{2x-2-\left(x-3\right)}{x-3}\)
\(\Rightarrow P=\dfrac{2x^2-6x+x^2+3x-3x^2-3}{\left(x+3\right)\left(x-3\right)}:\dfrac{2x-2-x+3}{x-3}\)
\(\Rightarrow P=\dfrac{-3x-3}{\left(x+3\right)\left(x-3\right)}:\dfrac{x+1}{x-3}\)
\(\Rightarrow P=\dfrac{-3\left(x+1\right)}{\left(x+3\right)\left(x-3\right)}.\dfrac{x-3}{x+1}\)
\(\Rightarrow P=\dfrac{-3}{x+3}\)