The measures of three angles of a quadrilateral are 80, 90, and 103 degrees. find the measure of the fourth angle.
a) 67
b) 77
c) 87
d) 97

C)87

Explanation:

the total sum of the internal angles of a quadrilateral is 360 degrees. Therefore, we must have:

(1)

In this problem, we know three of the angles:

so, we can re-arrange eq.(1) to solve for d, the missing angle:

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b