(3-9)  Cormorant has become negatively charged (with charge q-)after an unfortunate tangle with a van der Graaf generator. Nefertiti, standing at a distance x0 away from him, holds up a positively charged plate (charge q+) which causes Cormorant to be dragged towards her.  

Coulomb’s law is F = keq+q-/r2;  where ke is Coulomb’s constant and r is the distance between the charges. 

Use this to find an expression that would allow you to estimate the work done on Cormorant to bring him to a distance of x1 from Nefertiti’s plate (obviously we are ignoring lots of other factors like air resistance here but, frankly, Cormorant doesn’t care).