Answer:
E = 0.1472 J
Explanation:
Given that,
The number of turns in the solenoid, N = 2100
Area of the solenoid, A = 10 cm² = 0.001 m²
The length of the solenoid, l = 30 cm = 0.3 m
Current in the solenoid, I = 4 A
We need to find the magnetic energy stored in the solenoid. The expression for the stored energy is :

Where
L is self inductance of the solenoid,

So,

So, 0.1472 J of energy is stored in the solenoid.
The question is missing, however, I guess the problem is asking for the value of the force acting between the two balls.
The Coulomb force between the two balls is:

where

is the Coulomb's constant,

is the intensity of the two charges, and

is the distance between them.
Substituting these numbers into the equation, we get

The force is repulsive, because the charges have same sign and so they repel each other.
The particles that are usually in a much higher energy usually comes from the magnetic field of the Earth in which it is trapped consisting the Van Allen radiation belts. In addition to that, these radiation belts are somewhat essential because it protects satellites orbiting the Earth from the Sun's high energy radiation.
Because electrons are the only piece of the atom that is outside of the nucleus. the protons and neutrons are inside the nucleus.
then also the electrons itself have the charge to begin with