Step-by-step explanation:
Given that,
Charge 1,

Charge 2,

Distance between charges, r = 3.18 cm = 0.0318 m
(a) Let F is the magnitude of force that each sphere experiences. The force is given by :


(b) The spheres are brought into contact and then separated to a distance of 3.18 cm. When they are in contact, both possess equal charges. Net charge is :

Electric force is given by :

Hence, this is the required solution.