In how many ways can 3 identical red balls, 3 identical green balls, and 3 identical blue balls be arranged in a 3x3 grid, such that each row and each column of the grid contains 1 ball of each color?
There are 3! ways to chose the first row
For each of those there is 2 ways to chose the second row.
Then the last row is fixed.
So how many is that ?