Beginning Algebra With Applications, Chapter 2, 2.3, Section 2.3, Problem 86

Translate the phrase "twenty minus the sum of four-ninths of a number and three" 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{The sum of four-ninths of the number and thrice: } \frac{4}{9}n+3 && \text{Use the assigned variable to write an expression for any other unknown quantity.}\\
\\
&= 20 - \left( \frac{4}{9}n + 3 \right)&& \text{Use the assigned variable to write the variable expression.}\\
\\
&= 20 - \frac{4}{9}n - 3\\
\\
&= 17 - \frac{4}{9}n
\end{aligned}
\end{equation}
$