Number of spheres surrounding a tetrahedral void

The same question, asked 2 times: 10 May 2023 S2, 11 Apr 2026 S1. Every wording below, oldest first.

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Question 1
10 May 2023 S2
90 $What is minimum number of spheres required to develop a tetrahedral void?$
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Question 2
11 Apr 2026 S1
18 $What is the total number of spheres that surrounds the tetrahedral hole in the close-packed three-dimensional structure?$
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