The area of a circle is determined by pir^2 (remember that the exponent belongs to the radius). We can use 3.14 for pi. So, the new expression would be 3.14*r^2.
I'm assuming that when you said "The has a diameter of 2 feet", you are talking about the tree. If that is the case, you need to subtract the area of the tree from the area of the pile of leaves. Let's begin by calculating the areas using 3.14*r^2.
Area of tree: 3.14 ft^2
3.14*r^2
We need to find the radius, not the diameter. The radius is half of the diameter so we can take half of the diameter, which is 2 feet, to get 1 feet.
3.14*1^2
3.14*1
3.14
Area of circle of leaves: 452.16 ft^2
3.14*r^2
Again, we need the radius, not the diameter. So, we can take half of the diameter, 24 feet, to get 12 feet.
3.14*12^2
3.14*144
452.16 feet
Now, we can subtract.
452.16-3.14=449.02 ft^2