Read data from SQL when a field changes value and post the value in another field

Create a JQuery script that detects whether the Formidable Form field is changed or initiated.
Write a PHP script to accept the field value from the form and used the value to retreive data from a table. Calculations can be performed in the PHP script if needed. Encode the result in Json and return the value to the web page’s JQuery script.
The JQuery script will then output the retreived value in the appropirate field in the form.