JSFiddle - React, Tailwind, and code Playground

HTML

<input id="radio-1" type="radio" name="rmr" value="1"> 
<label for="radio-1">£3</label> <input id="radio-2" type="radio" name="rmr" value="2">     
<label for="radio-2">£5.5</label> 
<input id="radio-3" type="radio" name="rmr" value="4"> 
<label for="radio-3">£10</label>  
<div class="total-text" style="font-size:36px">£10</div>

JavaScript

$().ready(function(){
    var total = parseInt($("div.total-text").text().substring(1), 10);  
$("input[name='rmr']").bind('change', function() {     
  var amount = 0;     
  switch (this.value) {     
          case "1":         
                      amount = 3;         
                      break;     
          case "2":         
                      amount = 5.5;                          
                      break;     
          case "4":         
                      amount = 10;         
                      break;     
  }      
  $("div.total-text").text("£" + (total + amount)); 
  }); 

});