do the same thing here. when you want to find the derivative with respect to , say, just imagine that everything else is a constant, and differentiate as you normally would
see? can you apply this to what you are doing?
maybe "y" was a bad letter to use, because it is usually used to mean "a function of x". that is not how it is meant here. it is just some other variable that is treated as a constant when differentiating with respect to x
so now can you try the problem to make sure you get it