A small object carrying a charge of -7.50 nC is acted upon by a downward force of 30.0 nN when placed at a certain point in an electric field. a) What are the magnitude and direction of the electric field at the point in question? b) What would be the magnitude and direction of the force acting on a proton placed at this same point in the electric field? For part (a), I got E=4 N/C. But I do not know how to find the part (b).

A small object carrying a charge of -7.50 nC is acted upon by a downward force of 30.0 nN when placed at a certain point in an electric field. a) What are the magnitude and direction of the electric field at the point in question? b) What would be the magnitude and direction of the force acting on a proton placed at this same point in the electric field? For part (a), I got E=4 N/C. But I do not know how to find the part (b).