Three forces act on mass here
1. Tension in the thread (along the thread)
2. mg weight of the mass particle (downward)
3. Electric force F=QE due to horizontal field
Let the angle between thread and vertical be  \alpha   
Then use sine law
T= \frac{mg}{sin(90+ \alpha )}= \frac{QE}{sin(180- \alpha )}
m=10^{-3} Kg
QE=mg(tan( \alpha ))
Q= \frac{mg(tan( \alpha ))}{E}
the length of thread is 40 cm
But the distance from the vertical cannot be 224 cm please check ur question
any way this would help u