AMC 12 2008a Problem 18

A triangle $\triangle ABC$ with sides $5$, $6$, $7$ is placed in the three-dimensional plane with one vertex on the positive $x$ axis, one on the positive $y$ axis, and one on the positive $z$ axis. Let $O$ be the origin. What is the volume of $OABC$?

$\mathrm{(A)}\ \sqrt{85} \mathrm{(B)}\ \sqrt{90} \mathrm{(C)}\ \sqrt{95} \mathrm{(D)}\ 10 \mathrm{(E)}\ \sqrt{105}$