The electric field is formed by a charge of Q = 500 nC, the dialectic permeability is 1.5! Determine the potential

The electric field is formed by a charge of Q = 500 nC, the dialectic permeability is 1.5! Determine the potential difference of points a and at remote from the charge r1 = 20cm r3 = 2 meters? What work is done when the charge moves q = 2nC between these points

By definition of electric potential: φ = 1 / 4πέέ0 * q / r where έ is the dielectric constant of the medium, έ0 is the electric constant, q is the charge, r is the distance.
Then the potential difference U is equal to:
U = 10 ^ -10 * 500 * 10 ^ -9 / 1.5 * 0.2-10 ^ -10 * 500 * 10 ^ -9 / 1.5 * 2 = 5 * 10 ^ -17 (1/0 , 3-1 / 3) = 1.5 * 10 ^ -16
Work is determined by the formula: A = q * u
A = 1.5 * 10 ^ -16 * 2 * 10-9 = 3 * 10 ^ -25 J.