Problem with xsl attribute

[admin]

I have the fallowing xml code:
<table cellspacing="0" cellpadding="0" border="0">
<tbody>
<tr>
<td width="300" bgcolor="#ffffff">
<p> </p>
</td>
<td width="33" bgcolor="#ffffff">
<p></p>
</td>
<td width="135" bgcolor="#ffffff" >
<p></p>
</td>
</tr>

I need the width of the table but i've only the with of the td.
Someone have an idea how can i get the width of each td, to add their value and passing the result to the table attribute?