This is a hw problem so please explain your process instead of telling me the whole answer, thanks!

There is a conductive ball hanging from a string in a electric plate.

As you can see its slightly tilted toward the negative end.

mass of ball: 0.04g

potential difference: 480V

separation of plates: 0.06m

angle of string hanging: 20 degrees

the question asks:What is the charge of the ball?

I drew a free body diagram of three forces.

one: force of tension

two: gravity/weight

three: force of charge pointing towards the right

I think I'm suppose to add up the three forces to equal zero.

F1 + F2 + F3 = 0.

I think F3 should use the formula (C)(q1)(q2)/(r^2). Am I right?

If so then what is r???

I'm so lost in this problem please help guys!