Explanation

(b) The distribution of current is as shown in figure. As per question,
$\frac{i_{1}}{2} = 1\ or\ \ i_{1} = 2A$
In a closed circuit $ACFG$
$2i + 2 \times \frac{i_{1}}{2} - 4\left( i - i_{1} \right) = 0$
$7i_{1} = 4i$
or $i = \frac{7}{4}i_{1} = \frac{7}{4} \times 2 = \frac{7}{2}A$
Total resistance of the circuit between $A$ and $H$ is
$= 2 + \frac{4 \times 3}{4 + 3} = \frac{26}{7}$
EMF of cell is $E = \frac{7}{2} \times \frac{26}{7} = 13V$