Question

What is the force, in terms of Coulomb's constant, between two electrical charges of `-2 C` and `2 C` that are `3 m` apart?

Answer 1

`F=-4/9K`.

Explanation:

The Coulomb's force is given by

`F=K(Q_1Q_2)/r^2`

where `K` is the Coulomb's constant, `Q` are the charges and `r` the distance.

With your numbers we have

`F=K(-2*2)/3^2=-4/9K`.

Because you ask to keep it in units of the Coulomb constant, I will not continue the calculation evaluating `K`.
The negative sign tell us that the force is attractive because the two charges have opposite sign.