Charge on pith ball between two plates

[fizzicmaniac]

Homework Statement

The mass of the ball is 40 milligrams, the applied potential difference is 480 V and the plate separation is 6 centimeters. If the string hangs at an angle of 20 degrees to the vertical, determine the charge on the pith ball.

Homework Equations

[/B]
F=ma
E=F/q
V=E/d

The Attempt at a Solution

This is my work shown to the end, although the answer is wrong I'm not sure what I missed, and any help would be greatly appreciated. The answer is supposed to be 1.8x10^-8, but I'm not sure how to get there.
http://imgur.com/a/sgRUX

 

[haruspex]

V=E/d

Really?

 

[gneill]

Also:

The mass of the ball is 40 milligrams

Grams are not milligrams!