来,做数学题

everyday  a commuter takes a train that arrives at her station at precisely 6pm. She is met at the station by her hu*****and, who also arrives at precisely 6pm. He always drives the same route to the station and never varies his speed. One day the commuter takes an earlier train and arrives at the station at precisely 5pm. She decides to begin walking home along her hu*****and's usual route. They meet, she gets into the car, and they drive home. They arrive home precisely 10 mins earlier than usual . How long had the commuter been walking?