During stretching volume of wire remains same.

$\mathrm{R}=\mathrm{\rho }\frac{{\mathrm{L}}^2}{\mathrm{Vol}}$

Doubling the length will make the resistance 4 times.

New resistance of wire will become $12\mathrm{\Omega }$.

Resistance of one side of triangle will be $4\mathrm{\Omega }$.

$\text{ The net resistance}\text{:between two ends =}\frac{8\times 4}{8+4}=\frac{8}{3}\Omega$