The area of a circle is given by the formula:
A = πr^2, so in this case we have;
A = π 8^2 = 64π
If you're supposed to use a particular approximation for pi, then just substitute that and multiply.
For example, if the instructions say to use 3.14 for pi, then
A = 64(3.14) = 200.96 approximately.
Hope that helps!