Two people (A and B) want to meet each other to have lunch, and plan to meet at B's house party. A starts out for B's house, but when A is a mile away from B's house, B realizes that his house is a mess and A's isn't. So B takes off to meet A.

Once they meet, they talk for a while, and decide to meet at A's house instead. A goes back to her house to wait for B, and B goes to his house to pick up his food, then goes to A's house.
They arrive at A's house at exactly the same time. If B walks twice as fast as A, how far apart do the two people live?