Exception TypeError: must be str, not int in Python 3

Hello, I just joined a course about learning Python on Codecademy. I wrote a small function as below:

import numpy as np

def sumable(a ,b) :
  return a + b
  
msg = "Total your working days are: "
totalWorkingDay = sumable(10, 16)

print(str(msg + totalWorkingDay))

I want to learn about function, datatype, input & output in python. But When I was running the code above and got an exception TypeError: must be str, not int.

Traceback (most recent call last):
  File "main.py", line 10, in <module>
    print(str(msg + totalWorkingDay))
TypeError: must be str, not int

I know that str() function will help convert something datatype to string, but it didn't work for me.

I'm using Python 3.9 and Windows 11. Thanks for any idea.