JSFiddle - React, Tailwind, and code Playground

HTML

<select id="VatExpense">
        <option value="" disabled selected>Expense Type</option>
        <option value="0">Telephone</option>
        <option value="1">Public Transport & Taxis</option>
        <option value="0">Computer Consumables</option>
        <option value="0">Subsistence</option>
        <option value="1">Overseas Travel</option>
    </select>

<input type="text" id="vat" placeholder="Rate">

JavaScript

$('#VatExpense').change(function(){    
var selectedval = $(this).val();    
if(selectedval == 0){
  $('#vat').attr('placeholder','Standard rate 20%');
}else if(selectedval == 1){
 $('#vat').attr('placeholder','Zero Rate 0%');
}    
});