def adj_factor(original_size):
    """Calculates adjustment factor to resize images to 300x200

    This function uses the input tuple of original image size
    to determine image orientation, calculate an adjustment factor,
    and return a list of new width and height.

    Args:
        original_size (tuple): tuple of integers of orig width, height

    Returns:
        list: list of integers with newly-sized width, height
    """
    # Determine if vertical or horizontal pic, which way to scale
    if original_size[0] > original_size[1]:   # horizontal
        adj_factor = 300/original_size[0]
    else:                                     # vertical or square
        adj_factor = 200/original_size[1]
    new_sizes = []
    new_sizes.append(round(original_size[0] * adj_factor))  # New width
    new_sizes.append(round(original_size[1] * adj_factor))  # New height
    return new_sizes