calculating values from one database table and the textbox value

Question

hi friends ,
         i have created one windows form for leaves in this i have taken two textboxes and one for  number of leaves taken and one for leaves left for you,  in this i have to take data from database table that have column (maximum leaves)  which i had you used it in another form textbox(maximum leaves) having for different leave types(textbox). And i have to calculate maximum leaves - (minus) number of leaves,  that should give reaming leaves which you had left, when i select leave type and entering number of leaves it should calculate maximum leaves - number of leaves (which i entered). please  give some suggestion how to do.

thanks