What's the surface area of the box?

-- The top and bottom are each 3" x 5" = 15in² each.

-- The front and back are each 9" x 5" = 45in² each.

-- The left and right sides are each 3" x 9" =27 in² each.

-- So the whole thing is (2 x 15in²) + (2x 45in²) + 2x (27 in²) = 174 in² .