What is the force, in terms of Coulomb's constant, between two electrical charges of 2 C and -14 C that are 15 m  apart?

The force between two charged particles a distance $r$ $m$ apart is given by $F = \frac{k {q}_{1} {q}_{2}}{r} ^ 2$ where $k$ is Coulomb's constant. The answer is $F = \frac{k \cdot 2 \cdot \left(- 14\right)}{15} ^ 2 = \frac{- 28 k}{15} ^ 2 = \frac{- 28 k}{225}$
I'm not sure I can add much more explanation on this one. We were asked for an answer 'in terms of Coulomb's constant', so we've left $k$ as $k$ rather than substitute in its value of $9.0 \times {10}^{9} N {m}^{2} {C}^{-} 2$.