problem: New York and Denver are in different time zones.  When it is noon in New York, it is 10 a.m. in Denver.  A train leaves New York at 2 p.m. (New York time) and arrives in Denver 45 hours later.  What time is it in Denver when the train arrives?
solution: 2 p.m. New York time is noon in Denver.  45 hours past noon is 21 hours past noon the next day, which is 9 a.m. the day after that.  Think about it this way - 48 hours would mean two full days, and 45 hours is 3 hours less than that, thus, 3 hours before noon is $\boxed{9\text{ a.m.}}$