search list items in listbox for a specific string and make it a selected item

 hello, i don't know how to search my listbox items for a string that i've elicit from my db and then make it the selected item.
Booksort.SelectedItem = dl.Tables[0].Rows[0]["BookSort"].ToString().Trim();
 
i know that this code is wrong but it shows the general idea.
p.s
i have an ajax control that is triggered by the selected index changed in a listbox, will i be able to trigger it with the selected item in the list according to my string from my db?
10x.
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