Mass per unit length \(\lambda=\frac{M}{l}\)

Hence mass of the part of length \((l-x)\) is given by \(m=\lambda(l-x)\)

\(\Longrightarrow m=\frac{M(l-x)}{l}\)

For this part\(-\)

\(T=m a=\frac{M(l-x)}{l} \times \frac{F}{M}\)

\(\Longrightarrow T=\frac{F(l-x)}{l}\)