a
Let $V_{1}, I_{1}$ be the voltage and current for Nichrome wire of length $2 L$ and cross-sectional area $A$
$V_{2}, I_{2}$ be the voltage and current for Nichrome wire of length $L$ and cross-sectional area $2 A$
According to Kirchhoffs law, $I_{1}=\frac{\left(V_{1}-V\right)}{R_{1}}$
$I_{2}=\frac{\left(V-V_{2}\right)}{R_{2}}$
where $\mathrm{R}$ is thee resistance of Nicrome wire, $R=\frac{\rho l}{A}$
Hence,
$R_{1}=\frac{\rho 2 L}{A}=2 R$
$R_{2}=\frac{\rho L}{2 A}=0.5 R$
since current entering from one end leaves from other end,
$I_{1}=I_{2}$
$\frac{8-V}{2}=\frac{V-1}{0.5}$
$V=\frac{6}{2.5}=2.4 V$