Pith is an insulator, so there is no reason the two balls would equalize their charges after contact. Only a small fraction would be transfered, and it is hard to say how much. They probably want you to assume the balls acquire equal charges of -4.8 uC after contact.
Divide the charge by the electron charge of 1.6*10^-19 C to get the number of extra electrons.
Your second question has been asked and answered elsewhere.
(#1) If two pith balls - one which is neutral and another which has a charge of -9.6 uC (micro-Coulombs) - are touched together, how many extra electrons will each ball have?
(#2) Charge q1 = 6 uC is at the origin, charge q2 = 7 uC is at y = 2m, x = 0, charge q3 = 1.5 uC is at y = -1 m, x = 0. What is the force on q2?
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