$$ \begin{cases} 2R&=2.4\ut{cm}\\m&=670\ut{kg}\\E_{\text{steel}}&=200\times10^9\ut{N/m^2}\\g&= 9.80665\ut{m/s^2}\end{cases} $$$$ {F\over A}= E{\Delta L\over L}, $$$$ \begin{aligned}\Delta L&={ FL \over A E} \\&={ mgL \over \pi R^2 E} \\&={ 67g \over 2880000\pi } L\\\end{aligned} $$$$\ab{a}$$$$ \begin{aligned}\Delta L&={ 67g \over 2880000\pi } L\\&=\frac{13140911}{4800000000 \pi }\ut{m}\\&\approx..