1 and 2 share the same line (a line equals 180°) if 1 = 100° then 180°-100°=80°
2=80°
bc and 4 also share a straight line. if bc=30° then 180°-30°=150°
4=150°
this can be checked by adding them all together. a circle is equal to 360°.
100°+80°+30°+150°=360°
San makes up the straight line that makes up 1 and 2 (as you can see I have already answered the question a million times over) and as it is a straight line it is 180° which is backed up by all of the double checked math.
