If the VBOXADDITIONS cd does not pop up in File Manager, Use File Manager to open the contents of the VBOXADDITIONS cd, then open a terminal there, by going to File Manager's menu and selecting 'Open Current Folder in Terminal'
If the VBOXADDITIONS cd does not pop up in File Manager, Use File Manager to open the contents of the VBOXADDITIONS cd, then open a terminal there, by going to File Manager's menu and selecting 'Open Current Folder in Terminal'