When Charges Q_a,q_b,and Q_c Are Placed Respectively at the Corners

Multiple Choice

When charges q_a,q_b,and q_c are placed respectively at the corners a,b,and c of a right triangle,the potential at the midpoint of the hypotenuse is 20 V.When the charge q_a is removed,the potential at the midpoint becomes 15 V.When,instead,the charge q_b is removed (q_a and q_c both in place) ,the potential at the midpoint becomes 13 V.What is the potential at the midpoint if both charges q_a and q_c are removed?

A) 13 V
B) 7 V
C) 5 V
D) 8 V