One of the property of a rectangle is
[tex]\text{opposite sides are equal}[/tex]
This implies that
[tex]8x-12=20[/tex]
Solvig for x we have
[tex]\begin{gathered} 8x=20+12 \\ 8x=32 \\ x=\frac{32}{8} \\ x=4 \end{gathered}[/tex]
Therefore, the value of x is 4
