Since both rectangles are similar, the following ratio must be fulfilled:
[tex]\frac{x+9}{14}=\frac{9}{6}[/tex]
By multiplying both sides by 14, we get
[tex]\begin{gathered} x+9=\frac{9\times14}{6} \\ x+9=21 \end{gathered}[/tex]
and by subtracting 9 to both sides, we have
[tex]x=12[/tex]
Therefore, the answer is 12.
