Answer:
x = 40
Step-by-step explanation:
According to the Supplementary Angles Theorem, set 4x - 20 and x equal to 180. Once done, combine like-terms to get 5x - 20 = 180. So, straight off the bat, we know that 5x has to equal 200 [bringing 20 over to the right side of the equivalence symbol], therefore 40 is equal to x.
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