Giải giúp e bài này vs ạ

$M=\left(\dfrac{3}{x-1}-\dfrac{7}{x+1}\right):\dfrac{-4x+10}{x\left(x+1\right)}\\
=\left(\dfrac{3\left(x+1\right)}{\left(x-1\right)\left(x+1\right)}-\dfrac{7\left(x-1\right)}{\left(x-1\right)\left(x+1\right)}\right).\dfrac{x\left(x+1\right)}{-4x+10}\\ =\left(\dfrac{3x+3}{\left(x-1\right)\left(x+1\right)}-\dfrac{7x-7}{\left(x-1\right)\left(x+1\right)}\right).\dfrac{x\left(x+1\right)}{-4x+10}\\ =\dfrac{3x+3-7x+7}{\left(x-1\right)\left(x+1\right)}.\dfrac{x\left(x+1\right)}{-4x+10}\\ =\dfrac{-4x+10}{x-1}.\dfrac{x}{-4x+10}\\ =\dfrac{x}{x-1}$

Vậy `M= x/(x-1)`