If the question is about 4 things out of 4, the answer is, obviously, 1.
If the question is about 4 things out of n, then the answer is nC4 = n!/[(n-4)!*4!], whose value will obviously depend on n.
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4
216
There are 210 4 digit combinations and 5040 different 4 digit codes.
There are 840 4-digit combinations without repeating any digit in the combinations.
There are 1 combination of 4 colours out of 4, 4 combinations of 3 colours out of 4, 6 combinations of 2 colours out of 4, 4 combinations of 1 colour out of 4. A grand total of 15 (= 24-1) combinations.