Electric potential energy of a pair of point charges

[Xenocite]

I did all I can, and I'm stressed out over this. Thus, here I am. :(

Here's the question (I substitute the numbers with alphabet letters):

>Two point charges of magnitude of A nC and -B nC are separated by D m distance.
>The acceleration of gravity is 9.8 m/s^2. The Coulomb constant, k, is 9x10^9 N*m^2/C^2.
>What is the potential energy of the PAIR of charges? Answer in units of J.

So, what I did was find the potential difference, V, between the 2 charges, q1 and q2, at their respective points which has the distance of D using the equation:

V1 = (k*q1)/D
V2 = (k*q2)/D

Then find the electric potential energy(EPE) for each charge with the equation:

EPE1 = V1 * q2
EPE2 = V2 * q1

*(EPE1 and EPE2 are basically the same number)

And the total potential energy of the 2 charges is:

EPE(net) = EPE1 + EPE2

Answer is negative because q2 is -B which has negative value x 10^-9

If anyone spot any error or have any idea of what I did wrong, please do tell. Perhaps, I missed a step of taking acceleration of gravity into account somewhere? Thanks.

 

[Hootenanny]

You have calculated the electrical potential energy, but what about gravitational potential energy?

 

[Xenocite]

I've just now received an email from my professor that this problem was canceled due to computer grading error. I believe what I did as correct though. Thanks for all the help :)