You can put this solution on YOUR website! Hint: Number of combinations = (Number of choices for the first slot)*(Number of choices for the second slot)*(Number of choices for the third slot)*(Number of choices for the fourth slot)
So say for instance you had 8 choices for each slot, then you would have 8*8*8*8 = 4096 possible combinations. Keep in mind that this is NOT the answer as it's only an example.