Question 993493
Area is (1/2) bh=20 sq ft.  Units will be feet for base and height.
bh=40 
h=40/b
b=40/h
As I interpret the question, anything on the below graph where both are positive will give a rational value for the area.  If they want possible combinations, you can use anything on this line, like 8 and 5 or 5 and 8 (all are interchangeable), (40/9) and 9, 20/9 and 18, sqrt (40) and sqrt (40), two irrational numbers, sqrt 80 and  sqrt (5).
{{{graph(300,200,-40,40,-40,40,40/x)}}}