Find the fluid force on the top side.

Fluid force is , where  is fluid pressure and  is area of the object.

The fluid pressure is , where is weight density of the liquid per unit of volume and  is depth of the object.

The weight-density of water is  pounds per cubic foot, so .

The top side of the rectangle is submerged in  feet of water.

.

The area of the rectangle is  square foot.

The fluid force on top side is .

Substitute  and .

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Find the fluid force on the bottom side.

The top side of the rectangle is submerged in  feet of water.

Fluid pressure is .

.

The area of the rectangle is  square foot.

The fluid force on bottom side is .

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The buoyant force is the difference between the fluid forces on the top and botom sides of the solid.

Substitute bottom side  and top side .

.

.

The buoyant force of the rectangular solid is .