Well the formula for this problem is A=3.14(pi) * radius * radius
So multiply 3.14 times 9 times 9. first multiply 9 with 9 you get 81 then you multiply 81 times 3.14 which equals 254.34. When you find the formula to this kinds of equations it's very easy all you have to do is plug in the numbers. Hope this helps :)
