3x/(x+2)÷（x-2)/(2x-2)=6
3x(2x-2)/(x+2)(x-2)=6
6x(x-1)/(x^2-4)=6
x(x-1)/(x^2-4)=1
x(x-1)=x^2-4
x^2-x=x^2-4
-x=-4
x=4