Problem

(L). Evaluate $\displaystyle\iint_\Omega \left(\frac{y-x}{y+x}\right)^4\,\mathrm{d}x\mathrm{d}y$, where $\Omega$ is the region in the first quadrant bounded by the lines $x+y=1$ and $x+y=2$. Answer. $\underline{\quad(13)\quad}$.