1/2g+-g= ?

Answer 1

Is the first term 1/(2g) or (1/2)g = g/2?

+(-g) is the same as -g.
Add the two terms, whatever they are.

Answer 2

Since g is a common factor, you may remove it and just do the "work" as normal arithmetic:

(1/2)g + (-g) = g * (1/2 - 1)