3. In an $8 \times 8$ grid, fill in different natural numbers so that each cell contains only one number. If a number in a cell is greater than at least 6 numbers in its row and at least 6 numbers in its column, then this cell is called a "good cell". Therefore, the maximum number of "good cells" is $\qquad$.
3. Solution: Since there are 8 numbers in a row, at most 2 numbers can be greater than the 6 numbers in the same row. Only when these two numbers are also greater than the 6 numbers in their respective columns, the cell is considered a "good cell". Therefore, there can be at most 2 "good cells" in a row, and in 8 rows, there can be at most $2 \times 8=16$ "good cells". It is possible to have 16 "good cells", and the example below shows 16 cells marked with "1" as "good cells".