Double Integrals · Challenge problem

Let $D$ be the region in the first quadrant ($x \ge 0$, $y \ge 0$) that lies inside the circle $x^2 + y^2 = 4$ and outside the circle $x^2 + y^2 = 2x$. Find the $x$-coordinate $\bar x$ of the centroid of $D$. Give an exact answer.