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Answer:
(x, y) = (7, -1)
Explanation:
The expression for x makes it easy to use that for substitution.
3(-7y) +y = 20
-20y = 20 . . . . . collect terms
y = -1 . . . . . . . . . divide by -20
-7(-1) = x = 7 . . . use y in the second equation to find x
The solution is (x, y) = (7, -1).