deduction Values

Question

i have a gridview in that 

 

CO_RoomRent as [Room Rent],

CO_ExtrbedAmount as [Extra Bed Amount],

CO_ExtrapersonAmount as [Extra Person Amount],

CO_TotalRoomRent as [Total Amount],

CO_TransactionAmount as [Transaction Amount]

those are the fields

now in textbox i will give discount percentage

using that percentage

deduct that percentage

display

remaining value display in gridview

 

desktop application

c#

sql server2008

please help me