Ravi walks to and fro to a shopping mall. He spends 30 minutes shopping. If he walks at a speed of km an hour, he returns home at 19.00 hours. If walks at 15 kin an hour, he returns home at 18.30 hours. How far must he walk in order to ret hours home at 18.15 hours? `17\ k m//h r` b. `18\ k m//h r` c. `19\ k m//h r` d. `17. 5\ k m//h r` e. none of these