when two angles are vertical, they are congruent to each other means they are equal to each other. So m∠A = m∠B
and m∠A = x , m∠B = 3x -60
So,
x = 3x -60
Now we solve this equation for x,
3x - x = 60
2x = 60
x = 30
Thus, the m∠A = 30 And m∠B = 3 (30) - 60 = 90 - 60 = 30
As, they are equal so, m∠A and m∠B is 30.
