Analyzing One-Variable Relationships in Context

To write the equation, let's begin by defining the variable. Let $x$ be the number of CDs in the rack. We know that the rack can fit $7$ more CDs and that it's full when there are $30.$ This means that $x+7$ CDs would fill the rack. $$\begin{array}{c}x+7=30\end{array}$$ Let's solve this equation. There are currently $23$ CDs in the rack.