How to generate subtotals in rtf template

Summary:

Requirement to show subtotals at the top of each source

Content (please ensure you mask any confidential information):

I have developed a template that looks like below. The red circled ares is where I want the subtotals of each source to display.

This is a snippet of the xml

So basically I am expected to show totals for Payables and Manual for the DR and CR column

How can I achieve this within the template?

Version (include the version you are using, if applicable):

Code Snippet (add any code snippets that support your topic, if applicable):