Refer to the figure shown below.
Because the sum of angles on a straight line is 180°, therefore
m∠2 + m∠x = 180°
125° + m∠x = 180°
m∠x = 180 - 125 = 55°
Because the sum of angles in a triangle is 180°, therefore
m∠1 + m∠x + m∠y = 180
60 + 55 + m∠y = 180
m∠y = 180 - 60 - 55 = 65°
Because the sum of angles on a straight line is 180°, therefore
m∠3 + m∠y = 180
m∠3 + 65 = 180
m∠3 = 180 - 65 = 115°
Answer: m∠3 = 115°
