Your request is ambiguous. Do you want to rewrite time in fraction in terms of minutes? Seconds? Nanoseconds?
I'm assumming that you want 1 hour, 40 minutes, 48 seconds written in terms of seconds:
1. In order to write a fraction in terms of a unit, you have to know a unit equivalent. Since you want to know the time in terms of seconds, you have to know the number of seconds in 1 unit of the highest unit.
The highest unit is hours. The unit you want to convert it to is seconds. So the question to ask (a.k.a unit equivalent) is "How many seconds are there in 1 hour?" 3600 seconds in an hour; this will be your denominator.
2. To rewrite the given time in terms of seconds, find out each component's equivalent in terms of seconds:
Written in terms of seconds is:
Because 3600 seconds is 1 hour; 40 minutes is 2400 seconds; 48 seconds is 48 seconds. The sum of the numbers will equal to 1 hour 40 minutes and 48 seconds.
3. Thus the fraction becomes:
Which simplifies to