[tex]\begin{gathered} \text{ We want to make a profit of 135! plus the base cost, the 40CDs should cost }160\text{ \$}.\text{ If x is the cost of each CD,} \\ \\ 40x=135+25 \\ 40x=160 \\ x=\frac{160}{40} \\ x=4 \\ \\ \text{ Then he should sell his CD's for 4\$} \end{gathered}[/tex]