Hello,
I am assuming the donut does not have a hole in this situation.
If so, this problem is simply finding the area of a circle, given the diameter.
The formula for the area of a circle is:
π

In this formula, r is the radius of the circle, which is 1/2 of the diameter of the circle. So, the radius is 1/2 of 4 inches which is (1/2)(4) = 2 inches.
So, we use the formula and our calculated radius to find the area of the donut.
π

= π

= 4π ≈ 12.57 inches.
The area of the donut is 12.57 inches. Hope this helps!