Proving and Applying Polynomial Identities Practice Test

A rectangle has width $a$ and height $a$. A vertical strip of width $b$ is removed from the right side, leaving a rectangle of width $a-b$ and height $a$. That remaining rectangle is then partitioned by a horizontal segment into two rectangles of heights $a-b$ and $b$.

Which polynomial identity applies here for all real $a$ and $b$?​

A rectangle with side lengths $x+y$ and $x+z$ is partitioned by one vertical and one horizontal segment into four smaller rectangles with side lengths $x$, $y$, and $z$ as labeled. Which expression represents the total area (true for all $x$, $y$, and $z$)?