Javascript Radio Buton Toplamı

<form .....
<div id="a">
<div class="b">
Soru 1
<input type="radio" value="5" name="x">
<input type="radio" value="10" name="x">
<input type="radio" value="15" name="x">
<input type="radio" value="20" name="x">
</div>
<div class="b">
Soru2
<input type="radio" value="5" name="y">
<input type="radio" value="10" name="y">
<input type="radio" value="15" name="y">
<input type="radio" value="20" name="y">
</div>
</div>
...../>