Why do you not want to answer this thread?(Your answer will be sent to Jeanette and Aytekin)
You can have this kind of function by using the Form Calculation widget and Update/Calculate Field Conditions. Here's a demo form from the calculation guide: .
Here are some helpful guides:https://www.jotform.com/help/259-How-to-Perform-Calculation-in-the-Formhttps://www.jotform.com/help/286-How-to-Pass-Field-Value-to-Another-Field
Hope that helps. If you have any questions, let us know. Thank you.