how can i get help with a problem...

The problem

how can i get help with a problem like this:

Find all values of x that are not in the domain of g. If there is more than one value, separate them with commas

g(x)=x^2-16x+63 over x^2+4

The value that are not in the domian of g are the values for 'x' that make

x^2 + 4 = 0

........

........

x1 = 2i

x2 = -2i

So, the values are '2i' and '-2i'.