Electrostatic force between two charged pith balls at equilibrium

[Inquiring_Mike]

Here is the question...
A pith ball of mass 1.5g is suspended along a string which is attached to a non movable point, when a pith ball of equal charge and mass is brought close to the original pith ball. A state of equilibrium is reached and the pith balls are 2.6cm apart and the string attached to the suspended ball makes an angle of 20 with the vertical. Calculate the electrostatic force.

I think that the electrostatic force would just be mgtan(pheta)... Is that right?

 

[Inquiring_Mike]

Thanks for the help!