Acharge q produces an electric field of strength 2e at a distance of d away. determine the electric field strength at a distance of 1/2d away.

The electric field strength of a point charge is inversely proportional to the square of the distance from the charge ... a lot like gravity.

If the magnitude of the field is (2E) at the distance 'd', then at the distance '2d', it'll be (2E)/(2²).  That's (2E)/4 = 0.5E .

e/c, where e is its total energy