need help with solution

An example of the experimental setup from the lab "Electrostatics and Coulomb's Law" is shown below. If the distance between the two pith balls r = 7, and the angle of one string with the vertical 0 =90. find the value of the electric charge (in nano Coulombs nC) on one of the pith balls. (Hint: remember to use mass "0.05 g" in kilograms during your calculation and make sure your calculator is set to "degrees"). g = 9.8 m/s2, and k = 8.99 x 109 N. in C2 Your answer should be of one decimal place