Step-by-step explanation:
Number of security doors = 3
Let P denote a successful pass and F denote a failed pass.
Sample space refers to a set of all possible outcomes.
If the first attempt to pass through a door is a failure, then the outcome is F.
If the second attempt to pass through a door is a failure, then the outcome is PF.
If the third attempt to pass through a door is a failure, then the outcome is PPF.
If the fourth attempt to pass through a door is a failure, then the outcome is PPP.