The problem goes as such:

$\displaystyle 4xy-2x+4=0$

Evaluate y' at the point (-2,1)

What I did was (I use 'D' since I'm not sure on the proper notation at the moment, but I want to say it's d / dx)

$\displaystyle D(4xy)-D(2x)+D(4)=D(0)$

$\displaystyle 4y'-2+0=0$

$\displaystyle \frac{4y'}{4}-2+2+0=\frac{0+2}{4}$

$\displaystyle y'= \frac{2}{4}$