Non-Exact Equation - Integrating Factor

Hey I've got a question here where I need to find an integrating factor to make an equation exact, but it's in two variables and I'm having trouble finding both values!

Quote:

For what values of m and n will $\displaystyle u=x^ny^m$ be an integrating factor for the differential equation

$\displaystyle (-12y+14x)dx + (4x-6x^2y^{-1})dy=0$

To do this i'm using the exactness formula $\displaystyle \frac{\partial M}{\partial y}=\frac{\partial N}{\partial x}$ Which gives me:

$\displaystyle -12(m+1)x^ny^m+14mx^{n+1}y^{m-1}=4(n+1)x^ny^m - 6(n+2)x^{n+1}y^{m-1}$

$\displaystyle -12(m+1)+14m=4(n+1)-6(n+2)$

$\displaystyle m=2-n$

But i'm not sure where to go from here to get another equation to find m and n. A push in the right direction would be awesome. Thanks for your help!

-Kasper