Reassure the interviewer that you can handle stress at work like a pro by learning how to prioritize, organize, and determine what needs your focus and attention first. Give a relevant example of how you got out of a sticky situation by being quick to respond and adjust. An answer like this will do, "I find it best do concentrate on remaining calm. When I run into a customer who's upset, it helps them to calm down if I'm calm and we can work together to resolve the situation."