Let weight used is $W _1$, extension $\ell_1$

$W_1$, $\ell_1$

$y =\frac{ W _1 / A }{\ell_1 / L } \Rightarrow W _1=\frac{ yA \ell_1}{ L } \quad \ell_1=3.2 \times 10^{-2}+20 \times 10^{-5}$

Observation $-2$

Let weight used is $W _2$ extension $\ell_2$

$W _2$, $\ell_2$

$y =\frac{ W _2 / A }{\ell_2 / L } \Rightarrow W _1=\frac{ yA \ell_2}{ L } \quad \ell_1=3.2 \times 10^{-2}+45 \times 10^{-5}$

$W _2- W _1=\frac{y A}{L}\left(\ell_2-\ell_1\right) \Rightarrow y=\frac{\left(W_2-W_1\right) / L}{y A\left(\ell_2-\ell_1\right)} $

$\left(\frac{\Delta y}{y}\right)_{\max }=\frac{\Delta \ell_2+\Delta \ell_1}{\ell_2-\ell_1}=\frac{2 \times 10^{-5}}{25 \times 10^{-5}} $

$\left(\frac{\Delta y}{y}\right)_{\max } \times 100 \% \quad=\frac{2}{25} \times 100 \%=8 \%$