PLEASE HELP!! :) Which of the following options would increase the electric force the most?

a. tripling the charge on one particle

b. changing the sign of one of the particles.

c. doubling the charge on one particle

d. doubling the charge on both particles

You are traveling in a car going at a constant speed of 100km/h down a long, straight highway. you pass another car going in the same direction which is traveling at a constant speed of 80km/h. as measured from your car's reference frame this other car is traveling at −20km/h. what is the acceleration of your car as measured from the other car's reference frame? what is the acceleration of the other car as measured from your car's reference frame?