Answer:
According the the "Triangle Sum Theorem', a triangles interior angels add up to 180 degrees.
Therefore, we should add all the given angles (which equal to 180 degrees):
*We want to find the variable, NOT a missing angle*
3x + 5x + 2x = 180°
Combine the like terms:
10x = 180°
Divide by 10 on both sides to get rid of whats beside the 'x':
x = 18°
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Now, whats the degree measure of angle YXZ?
Substitute!
3* (18) = 54°
So the correct answer is C)
Hope I helped!