Answer:
The net charge is 
Solution:
As per the question:
Mass of the plastic bag, m = 12.0 g = 
Magnitude of electric field, E = 
Angle made by the string, 
Now,
To calculate the net charge, Q on the ball:
Vertical component of the tension in the string, 
Horizontal component of the tension in the string, 
Now,
Balancing the forces in the x-direction:

(1)
Balancing the forces in the y-direction:

where
g = acceleration due to gravity = 
Thus


Use T = 0.1357 N in eqn (1):

