Answer:
10cm
Step-by-step explanation
Perimeter of the rectangle = 2(16+4) = 40cm
Assume the length of a side of the square as x.
Therefore the perimeter of ssquare can be wwritten as 4x.(all sides are equal in a square )
And we can build up a simple equation as
4x=40
When u simplify this equation,you get the x value as 10cm. That's the side length of the square.