Answer:
Let the total Number of piece be x
∴Length of x Number of pieces
\begin{gathered} = x \times \frac{4}{5} \\ = \frac{4x}{5} \end{gathered}=x×54=54x
So total Length of 40m will be used to make
\begin{gathered} \frac{4x}{5} = 40 \\ \implies \: x = \frac{ \cancel{40} \times 5}{ \cancel4} \\ \implies \: x = 10 \times 5 \\ \implies \: x = 50\end{gathered}54x=40⟹x=440×5⟹x=10×5⟹x=50
Hence , The Answer is 50