JSFiddle - React, Tailwind, and code Playground

HTML

<input id="priceTag" name="priceTag" type="text" value="">
<input id="priceTag1" name="priceTag" type="text" value="45">
<select id="designChoice" name="designChoice">
     <option>Choose--</option>
     <option value="yes">yes</option>
     <option value="no">no</option>
</select>

JavaScript

jQuery(document).ready(function($){

    var priceTag = $('#priceTag');        
    var selectedYes=false;
    $('#priceTag').on('change', function(){
        if($(this).val($("#priceTag).val() + $("#priceTag1").val());
        }

    });
});