Solution
= Solution
Here $y\geq0$, so the <absolute value> equals $y$. The <volume integral>, evaluated in <Cartesian coordinates>, is
$$
J=\int_0^1\int_0^x\int_0^{xy}xy\,dz\,dy\,dx.
$$
The integrand is constant with respect to $z$, giving
$$
J=\int_0^1\int_0^xx^2y^2\,dy\,dx
=\frac13\int_0^1x^5\,dx
=\boxed{\frac1{18}}.
$$