first you find the area of the half circle cut out. area of circle is pi*radius² ; therefore the area of half of the circle is that equation divided by two. you get around 39 for the area of the half circle or 25pi/2. then find the area of the triange which is 1/2(base)(height) or 1/2(18)(20)=180
then do 180-(25pi/2) which equals to about 140.73009
