What is the force, in terms of Coulomb's constant, between two electrical charges of ##-1 C## and ##-2 C## that are ##4 m ## apart?

Use that describes force between static electrically charged particles. In its scalar form the law is: ##F=k_e|q_1q_2|/ r^2## ##F=8.99×10^9 Nm^2 C^-2|(-1C)(-2C)|/( 4^2 m^2) = 1.12×10^9N## That is a large force, it should give you an idea how large a coulomb really is. It's a huge amount of charge

Use Coulomb's law that describes force between static electrically charged particles. In its scalar form the law is: ##F=k_e|q_1q_2|/ r^2## where ##k_e = 8.99×10^9 Nm^2 C^-2 ## Now substituting the given charges and distance of separation:

##F=8.99×10^9 Nm^2 C^-2|(-1C)(-2C)|/( 4^2 m^2) = 1.12×10^9N## That is a large force, it should give you an idea how large a coulomb really is. It's a huge amount of charge