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37/21 = (-2/7)*x+7*x+4 // - (-2/7)*x+7*x+4
37/21-((-2/7)*x)-(7*x)-4 = 0
(2/7)*x-7*x+37/21-4 = 0
-47/7*x-47/21 = 0 // + 47/21
-47/7*x = 47/21 // : -47/7
x = 47/21/(-47/7)
x = -1/3
x = -1/3
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