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21=x+(x+13)
We move all terms to the left:
21-(x+(x+13))=0
We calculate terms in parentheses: -(x+(x+13)), so:We get rid of parentheses
x+(x+13)
We get rid of parentheses
x+x+13
We add all the numbers together, and all the variables
2x+13
Back to the equation:
-(2x+13)
-2x-13+21=0
We add all the numbers together, and all the variables
-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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