He used the property of addition. Hope this helps. Please mark me as brainliest if I am right.
Answer:
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Step-by-step explanation:
Answer:

Step-by-step explanation:
Suppose numbers are <em>x</em> and <em>y</em>
<u>Product of </u><em><u>x</u></em><u> and </u><em><u>y</u></em><u> is </u><em><u>-2</u></em>
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And sum of <em>x</em> and <em>y</em> is <em>-1</em>

The answer is C because that's is a 90 degree angle. So you just subtract 70 from 90.
Supplementary angles will always add up to 180. If you had a straight line, and you drew another line across that line, the two angles on either side of that line would add up to 180 because a flat line is equal to 180 degrees.