At cheng's bike rentals, it costs $21 to rent a bike for 6 hours. how many dollars does it cost per hour of bike use?

If a large cloud encounters a colder air mass, it tends to rise up in the sky. On the other hand, the cold air mass sinks toward the surface. This happens because temperature is a property that affects the density of substances. Colder substances are denser than warm substances.

Step-by-step explanation:

https://www.slader.com/discussion/question/what-might-happen-if-a-large-cloud-in-the-sky-suddenly-encountered-a-colder-air-mass-with-a-temperat/