Explanation

(d) Current in silver voltmeter.
$i_{1} = \frac{m_{1}}{z_{1}t_{1}} = \frac{1}{\left( 11.2 \times 10^{- 4} \right) \times (30 \times 60)} = 0.5$ A
Current in copper voltmeter $i_{2} = \frac{m_{2}}{z_{2}t_{2}}$
$i_{2} = \frac{1.8}{\left( 6.6 \times 10^{- 4} \right) \times (30 \times 60)} = 1.51$ A
So, total current given by battery $i_{1} + i_{2} = 2.01$ A
Energy supplied by battery$= Eit$
$W = (12) \times (2.01) \times (30 \times 60)J = 4.34 \times 10^{4}$ A