Identical Point Charges (+30 μC) Are Placed at the Corners

Identical point charges (+30 μC) are placed at the corners of a rectangle (4.0 m × 6.0 m) . How much external energy is required to bring a charge of 55 μC from infinity to the midpoint of one of the 6.0-m long sides of the rectangle?

A) 22 J
B) 16 J
C) 13 J
D) 19 J
E) 8.0 J