Answer: when you have a keyboard and when you are typing the energy that you are giving by butting pressure on the key to send the letter to the screen and that voluntarily exchange is in the key. Sometimes when your typing when you press go, or return that is the voluntarily going into the computer, iPad, phone, Tv, Watch, and even a camera.
Explanation: For example: If you own a tulip farm and sell tulips at a farmer's market, you are voluntarily exchanging your time and expertise for money, and consumers are exchanging money for your goods and services. Both parties, you and the consumers, are better off because of the exchange. Explanation: