[extravert]

Попробовала сама. Объясните, пожалуйста, где моя ошибка.

<script type="text/javascript">
  
function calc() {

var type_exp1 = document.getElementById("type_exp1");
var type_exp2 = document.getElementById("type_exp2");
var type_exp3 = document.getElementById("type_exp3");
var type_exp4 = document.getElementById("type_exp4");
  
  for (var i=0; i < type_exp4.length; i++)
	    if (type_exp4[i].checked){
	           type_exp4+=+type_exp4[i].value;
	    }
	  
	var price_exp4= type_exp4;
	document.getElementById("result_exp4").innerHTML=price_exp4;
	
  
  
  //Result 
 
 var result = document.getElementById("result"); 
  
 var price_exp1 = 0;
 var price_exp2 = 0;
 var price_exp3 = 0;
 var price_exp4 = 0;
 
 var price = 0;
  
 price_exp1 += (type_exp1.checked == true) ? parseInt(type_exp1.value) : 0;
 price_exp2 += (type_exp2.checked == true) ? parseInt(type_exp2.value) : 0;
 price_exp3 += (type_exp3.checked == true) ? parseInt(type_exp3.value) : 0;
 price_exp4 += (type_exp4.checked == true) ? parseInt(type_exp4.value) : 0;
  
 price=  price_exp1 + price_exp2 + price_exp3 + price_exp4;
  
 result_exp1.innerHTML = price_exp1; 
 result_exp2.innerHTML = price_exp2; 
 result_exp3.innerHTML = price_exp3;
 result_exp4.innerHTML = price_exp4;
 result.innerHTML = price;
} 
</script>

<table width="600">
 
  
<tr> 
<td colspan="3" width="500"><input type="checkbox" onchange="calc()" value="1500" id="type_exp1" />test1</td>
<td width="200"><span id="result_exp1">0</span> руб.</td>
 </tr> 

<tr> 
<td colspan="3" width="500"><input type="checkbox" onchange="calc()" value="1500" id="type_exp2" />test2</td>
<td width="200"><span id="result_exp2">0</span> руб.</td>
 </tr> 

<tr> 
<td colspan="3" width="500"><input type="checkbox" onchange="calc()" value="1500" id="type_exp3" />test3</td>
<td width="200"><span id="result_exp3">0</span> руб.</td>
 </tr> 

  
  <tr> 
    <td width="200"><input type="radio" onchange="calc()" value="1500" name="type_exp4" id="type_exp4" />test4</td>
        <td width="200"><input type="radio" onchange="calc()" value="1500" name="type_exp4" id="type_exp4" />test4</td>
    <td width="200"><input type="radio" onchange="calc()" value="1500" name="type_exp4" id="type_exp4" />test4</td>

<td width="200"><span id="result_exp4">0</span> руб.</td>
 </tr>
  
  <!-- Итог --> 
 <tr>
 <td colspan="3" width="500" class="td_result">ИТОГО:</td>

 <td class="td_result"><span id="result">0</span> руб.</td>
 </tr>
  
  
  
</table>