A rectangular based pyramid would fit the given description
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Cylinder
The answer depends on the relative sizes of these shapes.
1 method is to multiply length times the width and the 2 method is to divide the rectangle into triangles and find the area of one of the triangles and multiply the area by two.
In 3d a hexagonal pyramid. In 2d, two hexagons. Or a six-pointed star (like a Star of David), a parallelogram plus lots more possibilities
A prism.