Solve for x
x=7
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x\times 15-21-12x=0
Subtract 12x from both sides.
3x-21=0
Combine x\times 15 and -12x to get 3x.
3x=21
Add 21 to both sides. Anything plus zero gives itself.
x=\frac{21}{3}
Divide both sides by 3.
x=7
Divide 21 by 3 to get 7.
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