3x/(x-3)² - x/3-x
=3x/(x-3)² +x/(x-3)
=3x/(x-3)² +x(x-3)/(x-3)²
=3x/(x-3)² +(x²-3x)/(x-3)²
=(3x+x²-3x)/(x-3)²
=x²/(x-3)²
m+2n/n-m + m/n-m - 2m/n-m
=(m+2n+m-2m)/(n-m)
=2n/(n-m)