Estimate the area of each circle use 3 to approximate 4 feet?

You don't mention whether the 4 feet is the circumference, diameter or radius.

The area of a circle is pi times the radius squared.

If 4 feet is the circumference, the area is about 1.3 feet squared.

If 4 feet is the diameter, the area is about 12.6 feet squared.

If 4 feet is the radius, the area is about 50.3 feet squared.