Answer:
add them together and set them equal to 180
Explanation:
They are both supplementary angles, so 15x+85+20x-10=180, so combine like terms=>35x+75=180
subtract 75 from both sides=>35x=105
divide both sides by 35 to get x alone=>x=3
plug that in for 20x-10
20(3)-10
=>60-10
=>50