Answer:
By the inscribed angle theorem, the measure of inscribed angles is half the measure of its intercepted arc, the inscribed angle measuring 100°.
Intercepts the arc measuring
so:


Subtract 99 from both sides

By the corollary 3 of the inscribed angle theorem, the opposite angle of a quadrilateral inscribed in a circle are supplementary so:

Subtract 96 from both sides

and,


The inscribed angle measuring c° intercepts the arc measuring (a+b)° so:




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