First of all you rearrange the problem so that the same variables are together (remember to keep the sign in-front of the coefficient with it)...
This would make the problem look like...
4x^2 / 8x^2 * 4x^2 /2x^2 -y^2 + 3y^2 + 4y^2 + 10xy - 9xy - 5xy
Now you would simplify the coefficients based upon the variable...
x^2 - 10y^2 - 4xy
Hope this helps! :)
