area of a circle is PI x r^2
2 = d/2 = 5.4/2 = 2.7 cm
using 3.14 for PI
3.14 x 2.7^2 = 22.89 square inches
360 degree in a circle, shaded area is 180 degree, which is 50%
so 22.89 x .5 = 11.45 cm^2
