thats kinda where i was heaed, but since the ray has no numbered angles, i am starting think she, ( the instructor) is tricking us with the mirrors. this may be a very simple geometry problem. since a triangle equals 180 deg you can label all three corners A,B, and C. lets call the corner near the unknwn angle C. the angle opposite C is also C. so the unkown angle is equal to A+B.
what do you think? does that make since?
thanks for this help, I really do appreciate it.

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'73 VW camper
'80 300td wagon