Hey there,
Your correct answer would be
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First reason: It is a very tight corner for it to be a HUGE number. This is a acute angel. It would have a low degree. It would be 49°.
Second reason: We do
74+51+y+6=180
Once it run's to 180, we can now know what number is missing.
74°+51°+49°+6°= 180°
Your correct answer is 49°
Hope this helps.
~Jurgen