Solve for x
x=3
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12-x-3x=0
Subtract 3x from both sides.
12-4x=0
Combine -x and -3x to get -4x.
-4x=-12
Subtract 12 from both sides. Anything subtracted from zero gives its negation.
x=\frac{-12}{-4}
Divide both sides by -4.
x=3
Divide -12 by -4 to get 3.
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