Dear aspirant,
This sum can be solved by the law of coulomb force of attraction. As I can't attach a pdf so I would explain you how to get this sum. This sums can be solved just by formulas.
Force=( k ×q1×q2)/r^2.
where q1 and q2 are charges and r is the distance between the charges.
The value of k is = 9×10^9.
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