k is the distance of the vertical translation.
Since you shifted the graph 7 units down, k will be equal to 7
So g(x) = (0.5)x - 7 is f(x) vertically translated 7 units down
If g(x) is obtained by shifting f(x) down by 7 units
meaning that
g(x)=(0.5)~~~~~7 units to the bottom from f(x)-k?
I can't explain but k=-7
it's g(x)=f(x)-(-7)
so the k=7.
f(x)-k=f(g)-7
the original function of f(x) is obtained by shifting f(g) 7 units down, or by -7
so x=7
