Option D: 21 in is the base length of the triangular base.
Explanation:
Given that a triangular pyramid with a height of 9 inches has a volume of 63 cubic inches.
The height of the triangular base is 6 inches.
We need to determine the base length of the triangular pyramid.
The base length of the triangular pyramid can be determined using the formula,
Substituting and
in the above formula, we get,
Simplifying the terms, we get,
Dividing both sides by 3, we have,
Thus, the base length of the triangular pyramid is 21 in
Hence, Option D is the correct answer.