1) Find dy/dx for $\displaystyle 4y^2 - xy = 2$

The given answer is; $\displaystyle y / (8y - x)$ but I don't understand how to get that. My procedure was;

$\displaystyle 4y^2 - xy = 2$

$\displaystyle 8y - (x + y) = 0 $

$\displaystyle 8y - x - y = 0$

And according to how the answer was gotten, that means I should move over the -y to the other side, followed by the 8y - x together. What I don't understand is why you can't subtract the 8y and -y first to make -7y and then move it over? And why is the 8y - x supposed to be moved together to the other side instead of separately?

2) Find dy/dx for $\displaystyle (x + y) / (2x - y) = 1$

I'm assuming you have to apply the quotient rule first, but can anyone tell me how it's supposed to look after the rule's been applied? I'm doing something wrong in my calculations.