Jeremy wants to go to the airport. If he leaves now and rides his bike at the constant speed of 10 km/h, he will get to the airport at 6 pm. If he leaves now and rides his bike at the constant speed of 15 km/h, he will get to the airport at 5 pm. He decides to leave now, but when he gets to his garage, he discovers that his bike has been stolen, so he must walk instead. If he can walk at a constant speed of 6 km/h, what time will he arrive?