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8=-x+3x
We move all terms to the left:
8-(-x+3x)=0
We add all the numbers together, and all the variables
-(+2x)+8=0
We get rid of parentheses
-2x+8=0
We move all terms containing x to the left, all other terms to the right
-2x=-8
x=-8/-2
x=+4
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