Electric Fields Question?

Jan 2013
1
0
Sphere A has a mass of 4.2*10^-2 kg and is tethered to a wall by a thin thread. Sphere a has an excess of 1.2 *10^12 electrons. Sphere B has a deficit of 3.5*10^12 electrons and is 0.23 m from Sphere A

a) determine the angle between the thread and the wall
b) determine the tension in the thread.

ANSWERS - a) comes to 2.5 degrees, b) is 0.41N [up the thread]

i'm really having trouble with the procedure of this question. so far, i know that q= Ne.

so Sphere A : q = (1.2*10^12)(-1.602*10^-19) = -1.92*10^-7 C
Sphere B : q = (3.5*10^12)(-1.602*10^-19) = -5.6*10^-7 C

but i don't know what to do next? thanks guys!