Plot the $u-v$ graph from the following values:

$u \left(cm\right)$	$250$	$200$	$150$	$120$	$100$	$80$	$70$
$v \left(cm\right)$	$60.9$	$65.2$	$73.2$	$84$	$96.5$	$127.5$	$166.5$

Find out the focal length from the graph.