In an experiment with a convex lens. The plot of the image distance...

In an experiment with a convex lens. The plot of the image distance $\left({v}^{'}\right)$ against the object distance $\left({\mu}^{'}\right)$ measured from the focus gives a curve ${v}^{'}{\mu}^{'} = 225$. If all the distances are measured in $cm$. The magnitude of the focal length of the lens is _____ $cm$.