Two equal charges q are placed at a distance of 2a and a third charge -2q is placed at the midpoint. The potential energy of the system is

• A

  $\frac{{\mathrm{q}}^2}{8{\mathrm{\pi \epsilon }}_0\mathrm{a}}$

• B

  $\frac{6{\mathrm{q}}^2}{8{\mathrm{\pi \epsilon }}_0\mathrm{a}}$

• C

  $-\frac{7{\mathrm{q}}^2}{8{\mathrm{\pi \epsilon }}_0\mathrm{a}}$

• D

  $\frac{9{\mathrm{q}}^2}{8{\mathrm{\pi \epsilon }}_0\mathrm{a}}$