Answer:
180°
Step-by-step explanation:
[tex] m \angle 3 = m \angle \: 4..(vertical \: \angle s)...(1) \\ now \\ m \angle 1 + m \angle 4 + m \angle 2 = 180 \degree\\..(straight \: line \: \angle s) \\ m \angle 1 + m \angle 3 + m \angle 2 = 180 \degree..[from \: (1)] \\ \purple {\boxed {\bold {m \angle 1 + m \angle 2 + m \angle 3 = 180 \degree}}} [/tex]
