In moving from point B in a particular circuit to point A, an electron gains 4 aJ of potential energy. What is the signed value of Vab, the voltage across points A and B, taking the + polarity sign at point A and the - polarity reference sign at point B. Note that the unit aJ is an atto-joule, that is 1 x 10^-18 J and the charge on an electron is -1.6 x 10^-19 C. Alson in moving from point A in a particular circuit to point C, an electron experiences no change in potention energy. What is the value of Vca?