Since the lines are parallel 5x + 15 is the same as angle 1 and 5x + 15 + 3x - 3 equal 180°
[tex]5x + 15 + 3x - 3 = 180[/tex]
combine like terms like x's and constants like -3 and 15
[tex]8x + 12 = 180[/tex]
subtract 12 from 180 to get 168
[tex]8x = 168[/tex]
divide by 8
[tex]x = 21[/tex]
