How to treat a y when deriving a function? My econ class gave these questions.
Find derivatives for the following functions:
$$g(z) = z + y + 15$$
$$f(z) = yz + 2y$$
I'm not sure how I should treat the $y$. Is it a function or a variable?
If it is a variable $g'(z)=2$ and $f'(z)=y+2$ but as a function $g'(z)=1+y'$ and $f'(z)=zy'+y+2y'$.

There are two options here. Either $z$ is a variable and $y$ is a constant, or $z=x+iy$. 
In that case,
$g'(z)=1$
$f'(z)=y$.
I think that would be the case given the course you are taking.
My answer is also assuming we are differentiating w.r.t to $z$.
