At the vertices of the square there are charges of the same name, the value of which

At the vertices of the square there are charges of the same name, the value of which is q = 2.0 nC. The side of the square is equal to d = 10 cm. The force of interaction between the charges located in the adjacent vertices of the square is equal to … μN.

Let’s translate all the values from given to the SI system:
d = 10 cm = 0.1 m.
q = 2.0 nC = 2 * 10 ^ -9 C.
The force of interaction between charges according to Coulomb’s law:
F = k * q1 * q2 / L², where k is the coefficient 9 * 10 ^ 9, q1 is the value of the first charge, q2 is the value of the second charge, L is the distance between them.
The distance between the adjacent vertices of the square will be the distance between the charges, i.e. L = d and q1 = q2.
With this in mind:
F = k * q1 * q2 / L² = k * q1 * q2 / d² = k * q² / d².
Substituting the numerical values, we get:
F = k * q² / d² = 9 * 10 ^ 9 * (2 * 10 ^ -9) ² / 0.1² = 3.6 * 10 ^ -6 N.
Answer: 3.6 * 10 ^ -6 N or 3.6 μN.