Step-by-step Solution:

Logic: The numbers in the figure follow a row-wise pattern where the middle number is derived from the outer numbers.

Formula:
\( \text{Middle Number} = 2 \times \left( \frac{\text{First Number}}{\text{Third Number}} \right) \)

Row 1:
Given numbers: 72, 24, 6
Check: \( 2 \times \frac{72}{6} = 2 \times 12 = 24 \). (Condition satisfied)

Row 2:
Given numbers: 96, 16, 12
Check: \( 2 \times \frac{96}{12} = 2 \times 8 = 16 \). (Condition satisfied)

Row 3:
Given numbers: 108, ?, 18
Apply logic: \( ? = 2 \times \frac{108}{18} \)
\( ? = 2 \times 6 \)
\( ? = 12 \)

Therefore, the missing number is 12.