Exposed surface area of joined cuboids
A solid is made by attaching a smaller cuboid on top of a larger cuboid. There is no overlap of volume
The lower cuboid has length L = 8 cm, depth W = 9 cm and height H = 5 cm
The upper cuboid has length l = 7 cm, depth w = 4 cm and height h = 3 cm
The whole l by w base of the upper cuboid touches the lower top. These two touching surfaces are internal
Coat every exposed face, including the underside of the lower cuboid