Five point charges, each of value +q are placed on five vertices of a regular hexagon of side L. What is the magnitude of the force on a point charge of value -q placed at the centre of the hexagon?

Among the five forces on five charges, two pairs (four) of forces are cancelled with each other since they are equal in magnitude and opposite in direction. The resultant force is due to a single force given below.
F = \frac{1}{4πε_0} \times \frac{q \times q}{L^2}
F = \frac{1}{4πε_0} \times \frac{q^2}{L^2} (attractive in nature)