Question 94119
Let's call the angle A.
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The measure of the supplement of this angle is 180 - A
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The measure of the complement of this angle is 90 - A
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The problem now tells you that the measure of the supplement of this angle (180 - A) is
60 less than 3 times the complement of the angle (90 - A). So we need to write 3 times the
complement and subtract 60 from it to get 3(90 - A) - 60.
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We can now set these two equal. That is:
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180 - A = 3(90 -A) - 60
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Do the distributed multiplication on the right side and the equation becomes:
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180 - A = 270 - 3A - 60
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On the right side, combine the 270 and the - 60 into 210 to make the equation:
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180 - A = -3A + 210
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Now subtract 180 from both sides to get rid of the 180 on the left side. The equation 
then becomes:
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-A = -3A + 30
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Now add 3A to both sides and you get:
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2A = 30
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and divide both sides by 2 to find that A is 15 degrees.
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Hope this helps you to find where you went astray.