Answer:
Step-by-step explanation:
The two interior same-side angles are supplementary, so ...
... (5x +15)° +(3x -3)° = 180°
... 8x +12 = 180 . . . . . . . . . divide by °, collect terms
... 8x = 168 . . . . . . . . . . . . subtract 12
... x = 21 . . . . . . . . . . . . . . . divide by 8
Obtuse ∠1 has the same measure as its corresponding angle, (5x+15)°, so is ...
... ∠1 = (5·21 +15)° = 120°
