Rashmi leaves office at 6.00Pm and catches a 6.30 pm local train that arrives in her town at 7.00 pm . Her father leaves home to pick up her at 7.00pm from the station as she gets off the train. Yesterday , Rashmi left her office early and took a 6.00 pm train and arrived at 6.30 pm .As her father was not there to pick her up,she started walking towards home. Her father left home at the usual time , saw her daughter walking, picked her up and drove home arriving there 10 mins earlier than usual. For how ling did rashmi walk before her father picked her up?
A]10min b]15 min c]20 min d]25 min