Since it is asking for g(-2), that means that we only have to worry about the equation g(x) = x^2+2x. When it asks for g(-2), that means you replace every "x" that shows up in the equation with -2.
So plugging in -2 for x we get g(-2)=(-2)^2+2(-2). Simplifying we get g(-2)=4+(-4). Now adding we finally get g(-2)=0
If we assume your letters range from A to Z and your digits from 0 to 9, you have 26 possibilities per letter and 10 per digit. This gives you 26^4*10^4 which is roughly 4 billion and a half.