How do I keep certain children nodes?

[aur3l14no]

For example, from the web page

<tr>
  <td class="a"> 10 </td>
  <td class="b"> ... </td>
  <td class="c"> ... </td>
</tr>
<tr>
  <td class="a"> 5 </td>
  <td class="b"> ... </td>
  <td class="c"> ... </td>
</tr>

I want to extract <tr>s whose child <td class="a"> contains a value greater than 7. I would also like to throw away <td class="c"> since it's irrelavant. The result should be like

<tr>
  <td class="a"> 10 </td>
  <td class="b"> ... </td>
</tr>

And finally the result is extracted to text "10 ...".

Is this possible? How should I do it?

I know that I can extract <tr> with XPATH //tr[td[@class="a"]/text()>7]. But how do I remove <td class="c">?

XPath seems unable to do that. Will "extract text" help? But the html tags are already thrown away when the extraction happens. Maybe I should just remove all <td class="c"> using "Execute JavaScript before change detection"?

Many thanks!