first we should find out how much is the sum of length and width : so we have to find 2 numbers with sum of 9 and least possible area. the numbers will be 1,8 and the area is
now let's find 2 numbers with sum of 9 and greatest possible area. they are 4 and 5. the area is:
the final answer will be the difference between these two areas
V ( cylinder ) = r² π h V ( cone ) = 1/3 r² π h A cone that fits exactly inside the cylinder has the volume: V ( cone ) = 1/3 V ( cylinder = 1/3 · 81 = 27 ft³