$ sudo apt-get update
$ sudo apt-get install rt4-extension-jsgantt 

rt4-extension-jsgantt is installed in your system.

Make ensure the rt4-extension-jsgantt package were installed using the commands given below,

$ sudo dpkg-query -l | grep rt4-extension-jsgantt *

You will get with rt4-extension-jsgantt package name, version, architecture and description in a table

rt4-extension-jsgantt package basic information: