Math Problem : G.14 Five rectangles of same area

It is considered such rectangles (including squares) as the length of each side is integers (measure is cm).
There are five kinds of rectangles of which the area is same.
Find the smallest area among such areas.
Noted that two rectangles which can overlap exactly should be considered as the same kind.

Answer

36 cm²

^{(=1 × 36 = 2 × 18 = 3 × 12 = 4 × 9 = 6 × 6)}