Question 663606
Starting with 
-17 - 2x = 6 - x
Group like terms
-17 - 2x + 2x = 6 - x + 2x
-17 = 6 - x + 2x
-17 - 6 = 6 - 6 - x + 2x
-17 - 6 = -x + 2x
Rewrite as addition 
-17 + -6 = -x + 2x
-23 = x
Post more questions if you need further clarity.
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