I dont know how to get to the answer please help A small 80

I dont know how to get to the answer please help

A small 80 g insulating sphere is suspended from point P by a silk thread that is 50 cm long. The sphere bears an unknown electric charge Q. A positive point charge q = +2.0 MuC is brought to a position directly below P, and the sphere is repelled to a new position, 30 cm to the right of q, as shown. The charge Q, in MuC, is closest to +1.5. +2.0. +2.5. +3.0. +3.5.

Solution

the angle with vertical is,

   @ = sin^-1[30/50] = 36.87 degrees

the tension in the thread is,

     Tcos@ = mg

             T = mg / cos@ = 80*10^-3*9.8 / cos36.87 = 0.98 N

The charge is calculated as follows:

        kqQ/r^2 = Tsin@

       [9*10^9][2*10^-6]*Q/[0.3^2] = 0.98*sin36.87

hence, the required charge is,

     Q = 2.94X10^-6 C

        = 3 uC    (approximately)

therefore, option D is correct answer.