As well as the previous answers are you could always use the Pull attrib as well:
<ol class="row" id="possibilities">
<li class="span6">
<div class="row">
<div class="span3">
<p>some text here</p>
<p>Text Here too</p>
</div>
<figure class="span3 pull-right"><img src="img/screenshots/options.png" alt="Some text" /></figure>
</div>
</li>
<li class="span6">
<div class="row">
<figure class="span3"><img src="img/qrcode.png" alt="Some text" /></figure>
<div class="span3">
<p>Some text</p>
<p>Some text here too.</p>
</div>
</div>
</li>