Answer
$-w^2y+yz+wz$
Work Step by Step
The given expression, $
(w^2y+yz-w^2)+(w^2-2w^2y+wz)
,$ simplifies to
\begin{array}{l}\require{cancel}
w^2y+yz-w^2+w^2-2w^2y+wz
\\\\=
(w^2y-2w^2y)+yz+(-w^2+w^2)+wz
\\\\=
-w^2y+yz+0w^2+wz
\\\\=
-w^2y+yz+wz
.\end{array}