Three 250-μC Charges Are Placed on Tiny Conducting Spheres at the the Ends

Three 2.50-μC charges are placed on tiny conducting spheres at the ends of 1.00 m-long strings that are connected at 120° angles as shown below. The magnitude, in N, of the force on the knot at the center is ​ ​

A) 0.
B) 3.75 × 10⁻².
C) 5.63 × 10⁻².
D) 6.50 × 10⁻².
E) 7.50 × 10⁻².