7x+12
8x+3
Because it is a horizontal line the two angles must add up to 180°
So add the two angles up together and set it equal to 180°
7x+12+8x+3=180
Add the two x’s 7x+8x=15x
Add the constants 12+3=15
You get 15x+15=180
Now subtract 15 from both sides
15x=165
Now divide by 15 to get x
X=11
