I'm having trouble with this question.

Find dy/dx by implicit differentiation.

(x+y)/(x-y) = 3x

First I use the quotient rule getting:

[(1 + y')(x-y) - (1 - y')(x+y)] / [(x-y)^2] = 3

Then I factor out y' and solve the equation for y' which gives me:

y' = [3x^2 - 6xy +3y^2]/[2x - 2y]

but the answer is:

[6x - 3y - 1]/[3x + 1]

not sure what i'm doing wrong so any help would be appreciated. thanks