Rent textbox

Question

   
  Rent Texbox

 Service Textbox

 Grossrent Textbox

 Tds  Textbox

 Netrent Textbox


i typed the  rent and service for example 2000 + 3000 5000 as Groos rent

then tds 200 net rent will be 4800.

i want to restrict serive tax should not be more as rent and tds should  not more than gross rent
 
 for that send the code.

help me.

Regds,
Narasiman P