В чём состоит операция деньги-товар-деньги?

1. What is that noise? Somebody is practicing the piano.
2. It’s late. I think I'll take a taxi.
3. The level, when water boils at sea, is 212 degrees Fahrenheit.
4. My brother is looking for a place to live. He is staying with me until he finds somewhere.
5. I lost my pen again. I am always losing things.