Use the formula for the surface area of a rectangular prism:
[tex]\sf A=2(wl+hl+hw)[/tex]
Plug in what we know:
[tex]\sf A=2((18\dfrac{1}{2})(5\dfrac{1}{3})+(4\dfrac{5}{6})(5\dfrac{1}{3})+(4\dfrac{5}{6})(18\dfrac{1}{2}))[/tex]
Multiply:
[tex]\sf A=2((98\dfrac{2}{3})+(25\dfrac{7}{9})+(89\dfrac{5}{12}))[/tex]
Add:
[tex]\sf A=2(213\dfrac{31}{36})[/tex]
Multiply:
[tex]\boxed{\sf A=427\dfrac{13}{18}~ft^2}[/tex]
