Answer 1

https://code.sololearn.com/Wi772Mr81mX8/?ref=app

Answer 2

You need to include the React libraries. https://www.sololearn.com/learn/11962/

Answer 3

Yosharu you have forgotten to include React and react-DOM library, not adding babel script directive and without using ReactDOM.render.

Check out this code, I tried to add the lib and other necessary for you.

https://code.sololearn.com/WVQxQqEaI6r1/?ref=app