TreeGrid Footer

firstly sorry if there is a similar post somewhere else. I have a purchased version of dhtmlx. I am not sure how you attach a footer with a total sum of a particalur column into a grid. I have had a look at the doc and do not quite understand them. I only have this bit of code so far



but not sure what to do next, any help would be great.

Please read this tutorial

And look at this sample in addition

And for sure your code must include the dhtmlxgrid_filter.js extension.