You are given a code:

def main_solution(x):
    return func_20(func_13('vtntsf', '_'), func_15(x))

Can you predict the output of `main_solution("cbx")` 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": "cbx"}, "ref_output": "v\u00ab_ct\u00bb_\u00abnb_\u00bbt\u00ab_xs\u00bb_f", "ref_code": "def main_solution(x):\n    return func_20(func_13('vtntsf', '_'), func_15(x))", "funcname": "main_solution"}
rule