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(12-x)/3 = 4.5 // - 4.5
(12-x)/3-4.5 = 0
(12-x)/3+(-4.5*3)/3 = 0
12-x-4.5*3 = 0
-x-1.5 = 0
(-x-1.5)/3 = 0
(-x-1.5)/3 = 0 // * 3
-x-1.5 = 0
-x-1.5 = 0 // + 1.5
-x = 1.5 // * -1
x = -1.5
x = -1.5
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