Solve for x
x=4
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12x-21+x=31
Add x to both sides.
13x-21=31
Combine 12x and x to get 13x.
13x=31+21
Add 21 to both sides.
13x=52
Add 31 and 21 to get 52.
x=\frac{52}{13}
Divide both sides by 13.
x=4
Divide 52 by 13 to get 4.
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