You are given a code:

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

Can you predict the output of `main_solution("vulzfhkd")` 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": "vulzfhkd"}, "ref_output": "v\u00ab_fu\u00bb_\u00ablk_\u00bbz\u00ab_vf\u00bb_\u00abht_\u00bbk\u00ab_ld\u00bb", "ref_code": "def main_solution(x):\n    return func_20(func_13(x, '_'), func_15('fkvtl'))", "funcname": "main_solution"}
rule