Looking at the table:
| 6 | 10 | 14 |
|---|---|---|
| 9 | 15 | 21 |
| 12 | 20 | ? |
Examining the rows, each row forms an arithmetic sequence:
Row 1: 6,10,14 with common difference 4
Row 2: 9,15,21 with common difference 6
Row 3: 12,20,? with common difference 8
Following this pattern: ?=20+8=28
Examining the columns to verify:
Column 1: 6,9,12 with common difference 3
Column 2: 10,15,20 with common difference 5
Column 3: 14,21,? with common difference 7
Following this pattern: ?=21+7=28
Alternatively, observing the structure as products:
Column 1: 6=2×3, 9=3×3, 12=4×3
Column 2: 10=2×5, 15=3×5, 20=4×5
Column 3: 14=2×7, 21=3×7, ?=4×7=28
Each column multiplies consecutive odd numbers (3,5,7) by the row position (2,3,4).
Therefore, the missing number is 28.