This can be broken into two shapes: a 12 by 12 square and a circle with a diameter of 12. Adding the 2 ft border increases it to a 14 by 14 square and a circle with a radius of 16 (2 on each side).
With border:
Area of square = 14*14 = 196 Area of circle = 3.14(8*8) = 200.96
Together = 396.96
Without border:
Area of square = 12*12 = 144 Area of circle = 3.14(6*6) = 113.04
Together = 257.04
This is a difference of 396.96-257.04 = 139.02 sq. ft.
