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51-(12*x) = x/3 // - x/3
51-(12*x)-(x/3) = 0
51-12*x-(x/3) = 0
51-37/3*x = 0 // - 51
-37/3*x = -51 // : -37/3
x = -51/(-37/3)
x = 153/37
x = 153/37
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