Question

explain why it is possible to draw more than two different rectangles with an area of 36 square units but it is not possible to draw more than two different rectangles with an area of 15 square units. The sides of the rectangles are whole numbers

Answer 1

15 only has 4 factors 1,3,5, and 15 so you can draw a rectangle that has dimensions 15 by 1 or 3 by 5. 36 has lots of factors:
1 and 36, 2 and 18, 3 and 12, 6 and 6, so you could draw a rectangle for each one of those factor pairs.