Please Help Understand Functions

[toxicxarrow]

Ok, got rid of the duplication. Still getting this error:

C:\Python\python.exe C:/Users/-----/Desktop/Test.py
Type numbers: 5

Error:
Traceback (most recent call last):
  File "C:/Users/Vadim/Desktop/Test.py", line 13, in <module>
    main()
  File "C:/Users/Vadim/Desktop/Test.py", line 10, in main
    calculate()
  File "C:/Users/Vadim/Desktop/Test.py", line 6, in calculate
    a = enterNumbers() + 1
TypeError: unsupported operand type(s) for +: 'NoneType' and 'int'

Process finished with exit code 1