Beginning Algebra With Applications, Chapter 2, 2.3, Section 2.3, Problem 76

Translate the phrase "the difference between nine times a number and twice the number" into a variable expression. Then simplify the expression.

$
\begin{equation}
\begin{aligned}
& \text{The unknown number: } n && \text{Assign a variable to one of the number quantities}\\
\\
& \text{Twice the number: } 2n && \text{Use the assigned variable to write an expression for any other unknown quantity.}\\
\\
& \text{Nine times the number: } 9n && \text{Again, by using the assigned variable to write an expression for any other unknown quantity. }\\
\\
&= 9n - 2n && \text{Use the assigned variable to write the variable expression.}\\
\\
&= 7n
\end{aligned}
\end{equation}
$