LEN, LEFT, and RIGHT are available through the Microsoft.VisualBasic.dll library.
In the Code Options tab of the properties of the Initialize page of your object, add Microsoft.VisualBasic.dll as an entry in the "External References" section, and add Microsoft.VisualBasic as an entry in the "Namespace Imports" section.
After that, you can begin to use the string manipulation functions available in the Visual Basic