Short Answer 
To analyze the situation of four entries, the first entry does not require an exit, but each subsequent entry requires one. Therefore, for four entries, a total of three exits are needed to allow for re-entries.
Step 1: Understand the Situation
When we analyze the situation, it starts with one initial entry. You can think of it like this: you are allowed to enter without needing to initially leave. Therefore, the first entry does not require an exit. All subsequent entries do.
Step 2: Count the Entries and Exits
For each time you enter after the first one, you have to exit first. With a total of four entries, we can break it down like this:
- 1st Entry: No exit needed.
- 2nd Entry: Must exit to re-enter.
- 3rd Entry: Must exit to re-enter.
- 4th Entry: Must exit to re-enter.
Step 3: Calculate the Total Exits
Now, you should tally up the total exits required for the four entries. Each time you enter after the first, it necessitates one exit. Thus, for four entries, you will have to:
- Exited 3 times (for the 2nd, 3rd, and 4th entries).
In conclusion, if you have entered four times, this means you have had to exit a total of three times to allow for the re-entries.