semiserkel area=25.12, so serkel area=50.24
serkel area=pi*radius*radius, so radius=root(50.24/pi)
50.24/3.14159265=15.9918887
radius=root=3.998985959
kleer teech want radius=4, so diameter=8
semiserkel rim-leng=half rim leng av serkel+diameter
=pi*radius+diameter
=radius*(pi+2)
=4*(5.14159265)
=20.5663706