Answer
All angles are 60°
Work Step by Step
1. Internal angles of a triangle have a sum of 180°
$ (2x-120) ^{\circ}+(x-30) ^{\circ}+( \frac{1}{2}x+15) ^{\circ}= 180 ^{\circ}$
2. Solve the equation for x
$2x+x+\frac{1}{2}x=180+120+30-15$
$3\frac{1}{2}x=315$
$x=90^{\circ}$
3. Then find other two angles by replacing x=90
$2(90)-120=60 ^{\circ}$
$(90)-30=60 ^{\circ}$
$180-60-60=60 ^{\circ}$
