It takes 1 hour to get to work.
It takes 20 minutes to get to the train station, and the rest of the trip is spent on the train that takes him to work. That means he is on the train for 40 minutes.
20 minutes is equal to 1/3 hour and 40 minutes is 2/3 hour
So from home to train station:
1/3 hour * 42mph = 14 miles
And from train station to work:
2/3 hour * 60mph = 40 miles
So how far does Mark live from his work place?
14 + 40 = 54 miles