phpDynamically Display Drop down depnds on another drop down

Hi
i have three drop downs one is company and projects this two are dyanmic drop downs from mysql and another one is static.
when i select first dropdown company it should dispaly the second drop values projects relate to that company 
then whn i select third drop down and on click submit it should display the corrosponding vaues in grid view 


Please help me out to solve this in php bec i am new to php