While performing an experiment for determining the focal length of a concave mirror by u-v method, a student recorded the given sets of the positions in cm of the object and the corresponding image on the bench as $$ (12,51), (18,54), (30,50), (48,34), (42,42) $$ and $$ (78,98) $$. She used an optical bench of length $$1.5\,\text{m}$$ and the mirror is fixed at the $$90\,\text{cm}$$ mark on the bench. The maximum acceptable error in the location of the image is $$0.2\,\text{cm}$$. The reading that cannot be obtained from experimental measurement and has been incorrectly recorded, for a mirror of focal length $$24\,\text{cm}$$, is