Thinking Mathematically (6th Edition)

$x=12^\circ$ The two angles are: $11\times 12^\circ-20^\circ=112^\circ$ $7\times12^\circ+28^\circ=112^\circ$
The two given angles form a straight angle, which means that they are equal. $7x+28^\circ=11x-20^\circ$ $48^\circ=4x$ $x=12^\circ$ The two angles are: $11\times 12^\circ-20^\circ=112^\circ$ $7\times12^\circ+28^\circ=112^\circ$