my daughter usually finishes school at 4:30pm, calls at the supermarket, then catches the 5pm train which arrives at our town station at 5:30pm. i leave home each day, drive to the station and pick up my daughter at 5:30pm, just as she gets off the train. one day last week my daughter was able to finish school about 5 minutes earlier than usual, decided to go straight to the station instead of calling at the supermarket, and managed to catch the 4:30 train, which arrived at our town station at 5pm. because i was not there to pick her up she began to walk home. i left home at the usual time, saw my daughter walking, turned round, picked her up and drove home, arriving there 16 minutes earlier than usual. for how many minutes did my daughter walk before i pick her up?