Observation one
From the markings on the diagram <1 = 60o The left triangle is at least isosceles. Therefore equal sides produce equal angles opposite them.
Now we have accounted for 2 angles that are equal (each is 60 degrees) and add up to 120 degrees. The third angle (angle 2) is found from this equation.
<1 + 60 + <2 = 180 degrees. All triangles have 180 degrees.
60 + 60 + <2 = 180
Observation 2
<2 = 60 degrees.
120 + <2 = 180
m<2 = 180 - 120
m<2 = 60 degrees.
Observation 3
m<3 = 120
<2 and <3 are supplementary.
Any 2 angles on the same straight line are supplementary
60 + <3 = 180
<3 = 180 - 60
<3 = 120
Observation 4
m<4 = 40 degrees.
All triangles have 180 degrees. No exceptions.
m<4 + 20 +m<3 = 180
m<4 + 20 + 120 = 180
m<4 + 140 = 180
m<4 = 180 - 140
m<4 = 40