First let's define some points for the function f(x) = 2^x:
Comparing the values of g(x) with f(x) in the same values of x, we can see that the function g(x) is 12 units lesser than the function f(x).
So the size of the shift from function f(x) to g(x) is 12 units.
Half this shift is 6 units, so let's plot a new function, shifted only 6 units down from f(x):