how to get combobox value in windwoform

Question

hello
 i my window form i have combo box and i bind with sql server

the combobox bind like this

combobox1.datasource=dt;
combobox1.valuemember="id"; 
combobox1.displaymember="name";


now when i select tha name in combobox how i get the id of selected name

plz help me