If 3(2x+5) - 4 = 17, what is the value of 2x+5?

Notice that the expression $2x + 5$ appears as a group, so you do not need to solve for $x$. Add 4 to both sides of $3(2x+5) - 4 = 17$ to get $3(2x+5) = 21$. Divide by 3: $2x + 5 = 7$. As a check, $x = 1$, and $3(7) - 4 = 17$. A common wrong answer is 21, which comes from stopping one step early, and another is 1, which is the value of $x$, not the value of the expression asked for. A third is $\frac{13}{3}$, from forgetting to add the 4 before dividing. Always re-read what the question asks for.