I don't understand how to solve this question:

Question 10 0 / 3 points A 1.1 g pith ball is suspended from a thread, A charged rod is then placed next to the ball (without touching the ball) and exerts an electrostatic force horizontally on the pith ball so that the ball is deflected to the right at an angle of 20 to the vertical. Calculate the electrostatic force on the pith ball. Charged rod Round your answer to have four decimal places. Do not include units in your