Elongation in \(I^{st}\) part
\(\Delta x_1=\frac{\text { Net force } \times L}{A Y}\)
\(=\frac{(3+2) F L}{A E}\)
\(=\frac{5 F L}{A E}\)
Elongation in \(II^{nd}\) part
\(\Delta x_2=\frac{(F-2 F) L}{A E}=-\frac{F L}{A E}\)
So net elongation
\(\Delta x=\Delta x_1+\Delta x_2\)
\(=\frac{5 F L}{A E}-\frac{F L}{A E}=\frac{4 F L}{A E}\)