In the rectangle shown below the two corners have charges q1=−5μC  and q2=+2.0μC  The work done in moving a charge +3.0μC From B to A  is (take 1/4πε0=1010   N−m2/C2 )

Work doneVA=1010−5×10−615×10−2+2×10−65×10−2=115×106 volt                       and  VB=10102×10−615×10−2−5×10−65×10−2=−1315×106 volt ∴WBA= QVA- VB=3×10−6115×106−−1315×106=2.8 J