How to calculate summery of table cloumn and bind to textbo

Question

i have a table with clolumns

Account            Amount

 MADHU               500

MADHU                1000

 AJAY                     2500

AJAY                     5000 

 

 

am  binding account values to dropdown list,

when i select account MADHU,

 

i want to bind total amount(1500) to text box

 

how to do this