In order to solve this problem, use the following equations and steps shown: \begin{align} &\cssId{Step1}{F = σ_{F} · \pi·\frac{d^2}{4} }\\[3px] &\cssId{Step2}{F = 2·10^8 ·\pi· \frac{0.008^2}{4}}\\[3px] &\cssId{Step3}{F = 10.05kN}\\[3px] &\cssId{Step4}{ε = \frac{σ_{F}}{E} }\\[3px] &\cssId{Step5}{ε = \frac{2·10^8}{69000}=2.899·10^-3}\\[3px] &\cssId{Step6}{ΔL = ε·L_{0} }\\[3px] &\cssId{Step7}{ΔL = 2.899·10^-3 · 125 = 362.3·10^-3 mm}\\[3px] \end{align}