SEE REENA ITS QUITE EASY.POT.DIF. BETWEEN A& B MEANS WE NEED TO GO THROUGH THE NETWORT FROM BTOA.SO WE ARE GOING IN THE DIRECTION OPPOSITE TO THE CURRENT.MOVING PAST R1 & R2 WE ARE MOVING FROM LOW POTENTIAL TO HIGH POTENTIAL(AS I MOVES FROM HIGH TO LOW) SO THERE IS AVOLTAGE GAIN =I(R1+R2)

MOVING PAST THE CELL WE MOVE FROM POSITIVE TO NEGSTIVE TERMINAL &HECE HAVE AVOLTAGE DROP=-V.

THEREFORE ANSWER EQUAL TO==I(R1+R2)-V.Vab MEANS Va- Vb.RATE ME PLZ!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!