calculate the tax based on line item total if TaxCode is present on Invoice document

Hello Experts,

I'm using the WFR version 11.1.1.9.0 and having a requirement that I need to fetch some line items from the Invoice document based on some specific keyword and need to calculate the tax amount for the same line items total amount.

WFR should not read the entire Total Amount and Total Tax amount from the Invoice.

Please advise how I can achieve this functionality using WFR.

Thanks

Sanjeev