5x+9=17x-4x+81
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Simplify and combine like terms
5x+9=17x+-4x+81
5x+9=(17x+-4x)+(81)
5x+9=13x+81
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Subtract 13x from each side
5x+9-13x=13x+81-13x
-8x+9=81
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Subtract 9 from each side
-8x+9-9=81-9
-8x=72
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And now divide each side by -8
-8x ÷ -8 = 72 ÷ -8
x = -9