## Prealgebra (7th Edition)

$\angle x\ and\ \angle z\ are\ 100^o$ $\angle y\ is\ 80^o$
When parallel lines are cut by a transversal, opposite interior angles are equal. $\angle y$ is equal to the $180^o$ angle. $\angle x$ and the $80^o$ angle are supplementary. $\angle x=180^o-80^o=100^o$ Corresponding angles are also equal. $\angle z=\angle x=100^o$