now, if the diameter of the "cylindrical" tube is 4 inches, then its radius is half that, or 2 inches,
[tex]\bf \textit{total surface area of a cylinder}\\\\
S=2\pi r(h+r)~~
\begin{cases}
r=radius\\
h=height\\
-----\\
r=2\\
h=8
\end{cases}\implies S=2\pi (2)(8+2)
\\\\\\
S=4\pi (10)\implies S=40\pi [/tex]
