In the rectangle of the above figure, the sides have lengths $$5.0 \ cm$$ and $$15 \ cm$$, $$q_1 = -5.0 \ \mu C$$, and $$q_2 = +2.0 \ \mu C$$. With $$V=0$$ at infinity, what is the electric potential at
(a) corner A and
(b) corner B
(c) How much work is required to move a charge $$q_3 = +3.0 \ \mu C$$ from B to A along a diagonal of the rectangle?