A rectangular pyramid has a volume of 1 comma 512 in cubed , a height of 12 in. , and a base length of 21 in. What is the width of its base?

The volume of a rectangular pyramid is V = ⅓ × (base length × base width) × height. Substitute the given values: 1,512 = ⅓ × (21 × width) × 12 = 84 × width. Dividing 1,512 by 84 gives a base width of 18 inches, so the correct choice is 18 in.

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