The formula for area of a circle is r² x π.
Since we know the diameter, we can firstly divide by 2 to find our radius.
4/2 = 2
Now that we know the radius, we can substitute it in and square the value.
(2)² x π
(4) x π
Since we're finding the area in terms of pi, we won't multiply by pi, giving us the answer of 4π.
Therefore, the area of the circle is equal to 4π.
Hope this helped! :)