You can
put this solution on YOUR website!A whole 3 sided triangle is equal to 180 so the two angels 15 and 85 are added with the third angel (x) and equals to 180 degrees.
15 + 85 + x = 180
Then you add the two numbers:
100 + x = 180
Subtract 100 from both sides:
100 + x = 180
-100 -100
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x = 80 <--- And you should get 80 for the third angel! Simple is that!