The resistance of a wire is ‘R’ ohm. If it is melted and stretched to ‘n’ times its original length, its new resistance will be:

if the length and area be l and A , then $R = \frac{\rho l}{A}$

if it is extended to n times ,  l' (new length ) =nl   and A' = $\frac{A}{n}$

New resistance = R' = $\frac{\rho l\text{'}}{A\text{'}}=\frac{n^{2}l}{A}=n^{2}R$