To determine what value the function `mystery` returns when called with a value of 4, let's analyze the function step-by-step.
The function `mystery` is a recursive function. Here's how it works:
1. If the number passed to the function is less than or equal to 1, the function returns 1.
2. If the number is greater than 1, the function returns the product of the number and the result of calling `mystery` with the number decreased by one.
Let's trace the function calls when `number = 4`:
1. `mystery(4)` is called. Since 4 is greater than 1, it calculates `4 mystery(3)`.
2. `mystery(3)` is called. Since 3 is greater than 1, it calculates `3 mystery(2)`.
3. `mystery(2)` is called. Since 2 is greater than 1, it calculates `2 mystery(1)`.
4. `mystery(1)` is called. Since 1 is equal to 1, it returns 1.
Now, we work our way back up the recursive calls:
1. `mystery(1)` returns 1.
2. `mystery(2)` calculates `2 1` and returns 2.
3. `mystery(3)` calculates `3 2` and returns 6.
4. `mystery(4)` calculates `4 6` and returns 24.
So, the value that `mystery` returns when called with a value of 4 is 24.
Thus, the correct answer is:
```
24
```
