The area of a circle formula is ( 3.14 x radius ²) To find the radius, all you have to do is to divide the diameter by 2 (40.5 ÷ 2) which is 20.25 . Then you square the answer (20.25 x 20.25) then you get 410.0625. The last step is to multiply that answer with 3.14 (410.0625 x 3.15) then your answer you get 1,287.59625. After you rounded it the number will be 1,287.60. Hope this helped!!