Find a CFG for a language
The hint is another way of describing the same language. For the two languages to be the same, one must have: $x=p$, $y=p+q$, $z=q+r$, and $w=r$. Notice that these do satisfy the constraints $y\gt x, z\gt w$ and $x+z=y+w$ provided that $q,r\gt 0$. Now the structure of the hint language makes it easy to write a grammar.

$S \to ABA$

$A \to aAb|ab$

$B \to bBa|ba$