Round trip in Hcm Process & forms

HI Experts .

I am working on hcm process & forms using adobeforms .

I designed table using using dropdown . ( Please refer screen shot ) .

If user selects wage type value from dropdown then it should automatically display the corresponding value of amount .

Please tell me how can i do this .

Is it possible to do  with round trip & sap_pa backend service only , I don't want to use custom backend service .

Thanks & regards .

Bhushan Ghule