The difference is 12
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
good luck