Display mathmatical results by using Camunda Forms/ using DMN table

Hello everyone,
How can I display a result of mathmatical process, using camunda forms or DMN table
I have 3 text/number box, in the fisrt box I have Product Quantity, in the second one I have Product Units Price and in the third one it is the Total Payment,
how can display automaticlly the Total Payment which is Product Quantity * Product Unit Price,