Hey there!
We'll do it in terms of Pi, as a variable, and in terms of pi as 3.14
We know that since the diameter is from one side to the other in a circle, dividing it by 2 will give you the radius - the distance to the middle. We plug in this radius to our area formula:
a =

a =

a = 9

If our area is 9 pi, we can multiply 9 by 3.14 to get an approximate value:
A = 3.14(9)
A = 28.26
Hope this helps!