Can some one please help me figure out how to calculate this styrofoam...

You must find the area of the circle
A = π r^2
The radius is half of the diameter, so divide 26 by 2. This equates to 13
A = π • 13^2
Multiply 13 times 13 (13^2) and it equals 169.
A = π • 169
A= 530.93
The answer is 530.93