Discover interview questions

The interview was pretty routine, you sit with everyone else there waiting to be interviewed, it's a big company and expanding rapidly when I first applied in 2013. They ask you about your customer service experience if you have any, if you think you can handle the volume of calls you'll be trained for (at least 70+ calls a day), where you see yourself in blank number of years and if you think you'll be with Discover for the long run. They also drug test you just FYI. Great company, great people, great benefits, decent pay with great room to make more but all the calls started giving me headaches shorty after I started and I left.

Describe the overall process of the credit card business chain. In which part does Discover make profits?