## Precalculus (6th Edition)

$(20x+10)^\circ=150^\circ$ $(3x+9)^\circ=30^\circ$
The sum of the two angle is a straight angle ($180^\circ$): $(20x+10)^\circ+(3x+9)^\circ=(23x+19x)^\circ=180^\circ$ $23x+19=180$ $23x=180-19=161$ $x=7$ $(20x+10)^\circ=150^\circ$ $(3x+9)^\circ=30^\circ$