The area of a circle is given by:
[tex]A=\pi\cdot r^2[/tex]Where r is the circle's radius. In this case we have a diameter of 8cm so the radius 4cm. Using pi=3.14 we have that the area of the circle is:
[tex]A=3.14\cdot4^2=50.24[/tex]So the area is 50.24 cm^2.