If 2(3x-1)+7 = 23, what is the value of 3x - 1?

The question asks for the value of the grouped expression $3x - 1$, so there is no need to solve for $x$. Subtract 7 from both sides of $2(3x - 1) + 7 = 23$ to get $2(3x - 1) = 16$. Divide by 2: $3x - 1 = 8$. Check by solving for $x$: $3x = 9$ and $x = 3$, and $2(8) + 7 = 23$. A common wrong answer is 3, which is $x$ itself and not the expression asked about. Another is 16, from stopping one step early. Re-read the question.