MRJ,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
</style>
<script>
window.addEventListener('DOMContentLoaded', function() {
var span = document.querySelectorAll('span');
span[0].textContent = [].reduce.call( span, function(sum, el, i) {
return sum + (el.textContent * !!i||0)
},0);
});
</script>
</head>
<body>
<span>abc</span>
<span>115</span>
<span>25</span>
<span>340</span>
</body>
</html>