Answer:
3F
Step-by-step explanation:
Force = k * x
so k = force/distance = F/2
if you were to duplicate the distance 2 times more, the F must also do so so that it's proportional
so F*2 = 2F but since it says additional 4cm, you will need to add the initial one and this one so that it's 6cm in total.
2F + F = 3F