The surface area of a rectangular solid (rectangular prism) is:
[tex]SA=2(lh+wh+lw)[/tex]For the given solid:
l= 4ft
w= 2ft
h=10ft
[tex]\begin{gathered} SA=2(4ft\cdot10ft+2ft\cdot10ft+4ft\cdot2ft) \\ SA=2(40ft^2+20ft^2+8ft^2) \\ SA=2(68ft^2) \\ SA=136ft^2 \end{gathered}[/tex]Then, the surface area of the given solid is 136 square feet