The surface area is the sum of all the areas in the given prims, then we have:
[tex]SA=72+72+48+48+2A[/tex]
Plugging the value for the surface area and silving for A we have:
[tex]\begin{gathered} 432=72+72+48+48+2A \\ 432=240+2A \\ 2A=432-240 \\ 2A=192 \\ A=\frac{192}{2} \\ A=96 \end{gathered}[/tex]
Now that we know the missing area we can know the missing dimension:
[tex]\begin{gathered} 96=8x \\ x=\frac{96}{8} \\ x=12 \end{gathered}[/tex]
Therefore the missing length is 12.
