in a rectangle, the opposite sides are of equal legnths
on one side, there are 6 stones
on the opposite side, there are the same number of stones (6)
(if you calculate then area=legnth times width, area=36, legnth of one sides=6, 36=6 times width divide 6, , 6=width, legnth=6, legnth=width=6)
the answer is 6 stones