How to increment or add the values in database from front end?

Question

Hello,
I am Chetan, I am a student, Currently I am doing GNIIT(Software Engineering) course from NIIT in Pune. Now, I am learning ASP.Net.
We have told to create a project on Ticket Booking. In which I have to accept value from user, store it in database and then increment that value by the next value.Means, If I am booking the tickets and I have 100 tickets & I sold 10 tickets of them & that will be get stored in database in a particular row & then if I sold another 5 tickets then it should show me the value that how much tickets I have sold & how much tickets I have still left. Means, I want to increment the ticket value by adding the new ticket value in the previous value & that addition will get displayed to the user.
            Hope you would have understand my problem. I am waiting for your hopeful reply,
                                                                                               Chetan.