C) 87
Explanation:
the total sum of the internal angles of a quadrilateral is 360 degrees. Therefore, we must have:
\(a+b+c+d+=360\) (1)
In this problem, we know three of the angles:
\(a=90\\b=90\\c=103\)
so, we can re-arrange eq.(1) to solve for d, the missing angle:
\(d=360-a-b-c-=360-80-90-103=87\)
