The approximate perimeter is 25.12 feet.
The outer edges of the concrete region form semicircles. The perimeter of a circle is called the circumference, and is given by the formula
C=πd
Since these are semicircles, the circumference is given by C=1/2πd.
There are 4 of these semicircles, so the total would be
C=4(1/2)πd
The diameter of each one is 4 feet:
C=4(1/2)(3.14)(4) = 25.12
