Two positive point charges +4.00 μC and +2.00 μC are placed at the opposite corners of a rectangle as shown in the figure. (k = 1/4πε0 = 8.99×109 N⋅m2/C2) (a) What is the potential at point A (relative to infinity) due to these charges? (b) What is the potential at point B (relative to infinity) due to these charges?