Redwood Customization :computation of Amount based on Quantity x amount DFF values in Smartform

Summary:

we created Amount and Quantity DFF (additional information) in Purchase_req_line and DFF information is displayed in the smartform for user data entry. (refer the attached screen shot)

Now the requirement is : value entered in price and quantity DFF field needs to multiplied & displayed in the Purchase_req_line.Curreny_amount field.

is it possible to achieve this ? From my end, i tried creating the new business rule but the computed values are not shown. (screen shot)

Screen shot below

Content (please ensure you mask any confidential information):

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

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