Check the picture below.
notice, we have three pair of sides, let's add them all up to get the area
[tex]\stackrel{\textit{left and right}}{2(8\cdot 14)}+\stackrel{\textit{front and back}}{2(3.5\cdot 8)}+\stackrel{\textit{top and bottom}}{2(3.5\cdot 14)}\implies 378~in^2[/tex]
