Updating Field in Suitelet SubList

We have developed a sublist for a Suitelet shown below.  We want the user to enter in the travel time (custrecord_wo_detail_tvltime) and based on certain criteria calculate and then populate the Travel Cost field in the sublist (custrecord_wo_detail_tvldoll) so the user can see the calculated value.

Does anyone know how to do this?

var WODetailResults = form.addSubList('custpageresults', 'inlineeditor', 'Billing Information');
 
var fldWONo = WODetailResults.addField('custrecord_wo_detail_wonumber', 'text', 'WO #');
fldWONo.setDisplayType('disabled');
     
var fldServTech = WODetailResults.addField('custrecord_wo_detail_tech', 'select', 'Service Tech:', 'employee');
fldServTech.setDisplayType('disabled');
 
var fldTvlTime = WODetailResults.addField('custrecord_wo_detail_tvltime', 'float', 'Travel Time (mins)');