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<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
</style>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
<script>
$(function() {
$( ".sepSt" ).each(function(i, el) {
$(".waper-catalog-row-col-4 span",el).appendTo($(".waper-catalog-row-col-3", el))
});
});
</script>
</head>
<body>
<div class="sepSt">
<div class="waper-catalog-row-col-3">
<span>text</span>
</div>
<div class="waper-catalog-row-col-4">
<span>другой text</span>
</div>
</div>
<div class="sepSt">
<div class="waper-catalog-row-col-3">
<span>text</span>
</div>
<div class="waper-catalog-row-col-4">
<span>другой text1</span>
</div>
</div>
<div class="sepSt">
<div class="waper-catalog-row-col-3">
<span>text</span>
</div>
<div class="waper-catalog-row-col-4">
<span>другой text2</span>
</div>
</div>
</body>
</html>