From Infinity. A point charge +Q is located at the origin while a second charge −2Q is at (0,3 d) A third charge +Q from infinity is then placed at (4 d,0) a. How much work must be done by an external force to put the third charge at its current location? [5 pts] b. What is the electric potential at point (0,−3 d) after placing the third charge at (4 d,0) from infinity?