a data modeling question

[aha123]

Just had a job interview with a bank. They asked me the following questions:

1. Their credit card offers reward points. They want to predict the total of the remaining reward points for all customers for next week, next month, next quarter. What methods do you recommend to do such prediction? What explanatory variables would you consider? I have no idea for what data they have.

2. The same question, but add one more scenario: reward points have expiration time. For example, if a point is not used after one year, it will expire.

I would really appreciate if you can share some thoughts about how to go about doing such prediction.