$ sudo apt-get update
$ sudo apt-get install banshee-extension-foldersync 

banshee-extension-foldersync is installed in your system.

Make ensure the banshee-extension-foldersync package were installed using the commands given below,

$ sudo dpkg-query -l | grep banshee-extension-foldersync *

You will get with banshee-extension-foldersync package name, version, architecture and description in a table

banshee-extension-foldersync package basic information: