you can go a variety of ways on this as it is a classic interviewing question. They are looking for consultative sales approach or something demonstrating need. This method is more aggressive without being too aggressive, Paint the picture of what there day will be like without the pen and focus on the headache it will be to not have the pen. This will have them focusing on much they need the pen and how you can provide a need to them by selling them something that is essential to making their every day life easier.