concatenate two textbox details

Hi team

I need a html code for displaying s.no(1,2,..5),name(a,b,c,,d,e),amount(100,200...500) in drop down menu and when the user selects from the drop down it needs to be displayed in the corresponding 3 text box.and in the final text box all the three text box values needs to be added and displayed .

Thanks
sany