Answer
$C(x)=8x^3$
Work Step by Step
The width of the outer surface is $x+2$
The length of the outer surface is $4x+2$
The height of the outer surface is $2x+4$
The width of the outer surface is $x$
The length of the outer surface is $4x$
The height of the outer surface is $2x$
The volume of a rectangular prism is
$C(x)=(Legth)(Width)(Height)\\=
(x)(4x)(2x)\\=8x^3$