You have the misfortune to own an unreliable clock. This one gains exactly 15 minutes every hour. It is now showing 2:00pm and you know that is was correct at midnight, when you set it. The clock stopped 7 hours ago, what is the correct time now?
Since the clock is gaining 15 minutes every hour, for every real hour that has passed, the clock will show 75 minutes. Since the clock shows 2.00pm, we know that 840 clock minutes have passed. This therefore equals 672 real minutes and hence 11 hours 12 minutes. The clock stopped 7 hours ago, therefore the time must now be 6.12pm. QED.