How much energy is necessary to place three +2.0-µC point charges at the vertices of an equilateral triangle of side 2.0 cm if they started out extremely far away? (k = 1/4πε0 = 9.0 × 109 N ∙ m²/C²)

a) 4.5 J

b) 5.4 J

c) 6.7 J

d) 7.6 J