Dang it looks confusing
Is that Geometry
The answers is 4mm for the side length of the cube.
Ok so I'll demonstrate in programming language python.
import math
def circle():
r = float(input("Enter r: "))
a = math.pi * r ** 2
print("Area of circle with r = {0} is {1
}cm2".format(str(r), str(a))
circle()