Answer:
C = 18°
Explanation:
You want the value of angle C in the given figure.
Remote interior angles
The angle marked X in the attachment is an exterior angle to the left triangle. As such, its measure is the sum of the remote interior angles, marked 30° and 51°.
X = 30° +51° = 81°
Isosceles triangle
The angle marked X is one of two congruent base angles of the isosceles triangle on the right. That means ...
C = 180° -2X = 180° -2(81°)
C = 18°
The value of C is 18°.