A mass carrying a positive charge q = 8.2 x 10^-6 C is hanging from the ceiling by a light thread. The whole of the right wall is negatively charged with a uniform surface charge density ? = - 2.4 x 10^-6C/m². If the tension in the thread is T = 10.8 N, what is the angle ? (in deg) that the thread makes with the vertical direction?