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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def sortable_sortkey_title(instance):
 """Returns a sortable title as a mxin of sortkey + lowercase sortable_title """

    title = sortable_title(instance)
    if safe_callable(title):
        title = title()

    sort_key = instance.getSortKey()
    if sort_key is None:
        sort_key = 999999

    return "{:010.3f}{}".format(sort_key, title)