Choose a model with a limiting daily rate

Enter all eight pairs without transforming $x$. The product-moment coefficient is $r=-0.5634407309\approx-0.563$. Plot the eight table pairs with hire period on the horizontal axis and daily rate on the vertical axis; see the comparison sketch. The rate drops rapidly initially, then levels off. The relationship is negative and curved; $r$ is not close to $-1$, so the original coordinates do not give a close negative linear fit.

Model C, $y=a+b/x$, allows the daily rate to approach a finite limiting value $a$ as $x\to\infty$. This matches the levelling-off pattern and the context of a daily hire rate.

Put $u=1/x$ and regress $y$ on $u$. With $b=S_{uy}/S_{uu}$ and $a=\bar y-b\bar u$, obtain $a=99.78746018$ and $b=47.07263415$. Thus $a=99.8$, $b=47.1$ (3 s.f.). The correlation of $u$ and $y$ is $0.9918587189\approx0.992$, close to $1$.