[jQuery] Insert class into td in a nested div.

[Adolfo]

I have a series of td's that reside within a nested div. the <td> has
no class value and I would like to inject a css class value.

<div class=x>
     <div class=y>
          <div class=z>
              <table><tr>
                 <td>x</td> want a class in these tds

how can I do this with jquery?