A wire of length $L$ and $3$ identical cells of negligible internal resistances are connected in series. Due to the current, the temperature of the wire is raised by $\Delta \mathit{\text{T}}$ $$in a time $t$. $N$ number of similar cells is now connected  in series with a wire of the same material and cross-section but of length $2L$. The temperature of the wire is raised by the same amount $\Delta \mathit{\text{T}}$ $$in the same time. The value of $N$ is

Hence, the correct answer is 6.