Answer:
The correct option is III: 4.5 cm.
Step-by-step explanation:
The area of a square is the following:
(1)
Where:
A: is the area
b: is the side of the square
We have that the area is 20 cm², hence by solving equation (1) for <em>b</em> we can find the side:

Therefore, the correct option is III: 4.5 cm.
I hope it helps you!
The answer to this question is D
The answer should be the 3rd one.