But as it happened, my airplane arrived at the airport 1 hour earlier. So I walked from the airport directly to my friend's house. On the way to her house, I met her driving to pick me up. I got into the car, and we drove me to the house. This way, I arrived at the house at 11:40.
How long did I spend walking? (The only thing known about my walking speed and my friend's driving speed is that they are different and they are constant.)