Answer:
k = -3
Explanation:
Generally, we determine k by observing 
the vertical translation of the original graph 
in this case it’s the graph of f 
and count the number of units by which it’s translated.
Checking the sign of k :
If the graph is translated up then k > 0
If the graph is translated down then k < 0
……………………………………………………………………
in order to get the graph of g ,the graph of f 
is translated 3 units vertically but down 
then 
k = -3