Amelia used 432 inches³ of gravel.
A cuboid is a three dimensional shape that has six faces, twelve edges and eight vertices.
According to the given problem,
Length = 24 inches
Width = 12 inches
Height = 12 inches
Volume of a cuboid = (l × w × h) cubic units
⇒ V = (24 × 12 × 12) cubic inches
⇒ V = 3456 cubic inches
Now, Amelia filled [tex]\frac{1}{8}[/tex] of volume with gravel.
Therefore, amount of gravel used = [tex]\frac{3456}{8}[/tex] cubic inches
= 432 cubic inches
Hence, we can conclude that Amelia used 432 cubic inches of gravel.
Learn more about cuboid here:
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