A semi-circle is half of a circle and the area of a circle of radius r is r2.
We know that the area of a circle is:
area of a circle = r2
A semi-circle is half of a circle. Therefore the area of a semi-circle will be:
area of a semi-circle = 1/2 r2
We know that the radius is 9ft. Pi is approximately 3.14 or 22/7.
Now you just have to plug in the numbers and you will find the area!