You are given a code:

def main_solution(x):
    return func_20(func_13('brt', '-'), func_15('ntb'))

Can you predict the output of `main_solution("vjttj")` 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": "vjttj"}, "ref_output": "b\u00ab-nr\u00bb-\u00abtt\u00bb\u00abb\u00bb", "ref_code": "def main_solution(x):\n    return func_20(func_13('brt', '-'), func_15('ntb'))", "funcname": "main_solution"}
rule