How Much Energy Is Necessary to Place Three $+ 2.0 - \mu \mathrm { C }$

How much energy is necessary to place three $+ 2.0 - \mu \mathrm { C }$ point charges at the vertices of an equilateral triangle of side $2.0 \mathrm {~cm}$ if they started out extremely far away? $\left( k = 1 / 4 \pi \varepsilon _ { 0 } = 9.0 \times 10 ^ { 9 } \mathrm {~N} \right.$ $\cdot \mathrm { m } ^ { 2 } / \mathrm { C } ^ { 2 }$ )

A) $6.7 \mathrm {~J}$
B) $5.4 \mathrm {~J}$
C) $4.5 \mathrm {~J}$
D) $7.6 \mathrm {~J}$