to find the area of a circle, you mutiply the Radius to the second power ( R x R ) and multiply that by Pi (3.14).
so, 4 x 4 = 16
16 x 3.14 = 50.24
so it should be 50 (simplified.)
now you convert these 50 inches into feet using the scale. every 1 inch is 3 feet. It should be 150 feet.
Hope this helps you understand how to find the area using the radius! Good luck!