AMC 12 2007a Problem 10

A triangle with side lengths in the ratio $3 : 4 : 5$ is inscribed in a circle with radius 3. What is the area of the triangle?

$\mathrm{(A)}\ 8.64 \mathrm{(B)}\ 12 \mathrm{(C)}\ 5\pi \mathrm{(D)}\ 17.28 \mathrm{(E)}\ 18$