Jquery select box set to "selected"

Hey, I have a select box with the id of “age”. I would like to have jquery set the correct age to selected. I have an invisible text box that has the age in it and javascript picks up the current age from this text box. Here is how the select box looks. My problem is getting the right <option> to be selected. Say for example purposes the <option> I want selected is 30. How would I go about getting it selected?

<select name="age" id="age">

<option value="20">20</option>
<option value="30">30</option>
<option value="40">40</option>


Thanks so much.

EDIT: Found the answer. All you have to do is: