You are given a code:

def main_solution(x):
    return (func_15('vtsxvu') + func_9('zpumxg'))

Can you predict the output of `main_solution("yjkztbypnr")` 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": "yjkztbypnr"}, "ref_output": "\u00abv\u00bb\u00abt\u00bb\u00abs\u00bb\u00abx\u00bb\u00abv\u00bb\u00abu\u00bbzpumxggxmupz", "ref_code": "def main_solution(x):\n    return (func_15('vtsxvu') + func_9('zpumxg'))", "funcname": "main_solution"}
rule