You are given a code:

def main_solution(x):
    return func_15(('vbo' + 'jxv'))

Can you predict the output of `main_solution("vupxng")` without writing any code? Please reason and put your final answer in the following json format: {"output": <your output>}, where <your output> should be the final string.
user
{"ref_input": {"x": "vupxng"}, "ref_output": "\u00abv\u00bb\u00abb\u00bb\u00abo\u00bb\u00abj\u00bb\u00abx\u00bb\u00abv\u00bb", "ref_code": "def main_solution(x):\n    return func_15(('vbo' + 'jxv'))", "funcname": "main_solution"}
rule