Since adding a constant to a function simply moved the graph upwards by that amount, solve f(x) for any value and see how much the graph given is different from that value of y...the simplest way in this case may be to simply find f(0) which is:
5*2^0=5
Clearly the graph at x=0 is at y=-2 so we can see that k is:
5+k=-2 so
k=-7
