Neutral metal sphere A, of mass 0.10kg, hangs from an insulating wire 2.0m long. An identical metal sphere B, with charge -q is brought into contact with sphere A. Sphere A goes 12 degrees away from Sphere B and there is a 90 degree angle at Sphere B between A and the hook of the insulating wire. Calculate the initial charge on Sphere B.

Question

Note: when one object with charge Q is brought in contact with a neutral object 1/2 the charge is transferred to the neutral object.

I don't understand how to do this.
Ans: 3.9x10^-6C