Answer:
29.4 uN
Step-by-step explanation:
The electric force between two charges can be calculated using Coulomb's Law. According to this law the force between two point charges is given as:

where k is a proportionality constant known as the Coulomb's law constant. Its value is
Nm²/C²
r = distance between charges = 70 cm = 0.7 m
q1 = q2 = 4nC =
C
The negative sign indicates that the charges are negative. In the formula we will only use the magnitude of the charges.
Using these values in the formula, we get:

Therefore, the magnitude of repulsive force between the given charges will be 29.4 uN