By hypothesis, There's 15 minutes between work and home. So going to work takes 15 minutes, and going back home from work takes 15 minutes, making a total of 30 minutes per day going back and forth to work.
Let x be the time spent in a 5 day work week travelling back and forth to work, using the rule of three:
1 day --> 30 minutes
5 days --> x minutes
x = (5*30)/1 = 5*30 = 150 minutes.
150 minutes = 150/60 = 2.5 hours.
So in a 5 day work week, the time spent travelling back and forth to work is 2.5 hours, or 150 minutes.
Hope this Helps! :)