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Rearrange Array: Negatives First

Write a function `re_arrange_array(arr, n)` that takes in an array `arr` and an integer `n`, and re-arranges the first `n` elements of the given array so that all negative elements appear before positive ones, while preserving the relative order among negative and positive elements.

#### Example Usage
```python [main.nopy]
re_arrange_array([-1, 2, -3, 4, 5, 6, -7, 8, 9], 9)
# Output: [-1, -3, -7, 2, 4, 5, 6, 8, 9]

re_arrange_array([12, -14, -26, 13, 15], 5)
# Output: [-14, -26, 12, 13, 15]

re_arrange_array([10, 24, 36, -42, -39, -78, 85], 7)
# Output: [-42, -39, -78, 10, 24, 36, 85]
```

#### Constraints
- The input array `arr` will contain integers.
- The integer `n` will be a positive integer less than or equal to the length of `arr`.
- The function should modify the array in-place and return it.
def re_arrange_array(arr, n):
    """
    Re-arranges the first n elements of the array so that all negative elements
    appear before positive ones, preserving their relative order.

    Parameters:
    arr (list): The input array of integers.
    n (int): The number of elements to consider for re-arrangement.

    Returns:
    list: The modified array with the first n elements re-arranged.
    """
    # Placeholder for the solution
    pass