A charged cloud system produces an electric field in the air near Earth's surface. A particle of charge -1.6 x 10-9 C is acted on with a downward electrostatic force of 4.5 x10-6 N when placed in this field. a) What is the magnitude of the electric field? b) What is the magnitude of the electrostatic force on a proton placed in this field? c) What is the gravitational force on the proton? d) What is the ratio of the electrostatic force to the gravitational force in this case?