The Surface area to be painted = 512 ft²
The surface area of a rectangular prism = 2(w × l + h× l + h × w). Where:
w = width of the rectangular prism
h = height of the rectangular prism
l = length of the rectangular prism
The block column has a shape of rectangular prism. Therefore, the surface area that Richard needs to paint which excludes the bottom of the block = 2(w × l + h× l + h × w) - l × w.
Plug in the values
Surface area to be painted = 2(8 × 10 + 12 × 10 + 12 × 8) - 10 × 8
Surface area to be painted = 592 - 80
Surface area to be painted = 512 ft²
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