Answers:
a = 217 degrees
The interior angle up top is 52 degrees
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Explanation:
The 143 degree angle and angle 'a' combine to form a full 360 degree rotation.
143+a = 360
a = 360-143
a = 217
The reflex angle 'a' is 217 degrees.
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Rule: The four angles of any quadrilateral always add to 360 degrees
This rule is similar to the idea that the angles of a triangle always add to 180 (in fact, the proof of the quadrilateral rule above uses this triangle rule).
With the quadrilateral rule in mind, we can find the missing angle up top. I'll call it angle b.
a+b+28+63 = 360
217+b+28+63 = 360
b+308 = 360
b = 360-308
b = 52
The interior angle up top is 52 degrees