Explanation:
The Coulomb's law states that the magnitude of each of the electric forces between two point-at-rest charges is directly proportional to the product of the magnitude of both charges and inversely proportional to the square of the distance that separates them:
In this case we have an electron (-e) and a proton (e), so:
In this case, the electric force is negative, therefore, the force is repulsive and its magnitude is: