A square is a shape with 4 equal lengthed sides. The perimeter is the sum of the lengths of the sides. Therefore for a square, the length of one side is a quarter of the perimeter.

In this example the perimeter is sqrt(120)cm, so the length of a side is [sqrt(120)]/4 cm.

The area of a square is just the length of on side squared, or multiplied with itself. So what we have is (sqrt(120)/4) ^{2 }= 120/16 = 7.5

In terms of units, the length is given in cm, and as the area is cm*cm it's unit is cm^{2}^{ }

So the answer is 7.5cm^{2}