In a triangle, the three interior angles always add to 180°
m∠1 = x+20
m∠2 = 2x+10
m∠3 = 4x-60
x+ 20 + 2x + 10 + 4x - 60 = 180
7x - 30 = 180
7x = 180 + 30
7x = 210
x = 210/7
x = 30
m∠1 = x+20 = 30 + 20 = 50°
m∠2 = 2x+10 = 2*30 + 10 = 70°
m∠3 = 4x-60 = 4 * 30 - 60 = 60°
