d. 5
step-by-step explanation:
f(x) + n - shift a graph n units up
f(x) - n - shift a graph n units down
f(x + n) - shift a graph n units to the left
f(x - n) - shift a graph n units to the right
on the picture we can see:
the graph g(x) was made by shifting the graph f(x), 5 units to the left.
therefore g(x) = f(x + 5) → k = 5
look at the picture.