Two Tiny Grains of Sand Having Charges of 4

Multiple Choice

Two tiny grains of sand having charges of 4.0 μC and -4.0 μC are situated along the x-axis at x₁ = 2.0 m and x₂ = -2.0 m.What is electric potential energy of these grains relative to infinity? (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C²)

A) -36 mJ
B) 36 mJ
C) 0 J
D) -72 mJ
E) 72 mJ