Failed to solve

[NormanAnderson42]

I finished the line 18 already but when the line 21 i write the command it show [fail to solve.]in the terminal.
How i can solve this? i try to install docker (in raspberry pi 4) what should i do ?
In readme

[alffykasum]

There are a few possible reasons why this might be happening:

There may be an issue with the network connection. Make sure that the machine has a stable connection to the internet, and try running the command again.

The package repositories may be experiencing some issues. Try running the command again at a later time to see if the problem persists.

There may be a problem with the package manager itself. Try running apt-get clean and apt-get autoclean to clean up the package manager's cache and see if that resolves the issue.

There may be an issue with the package sources list. Make sure that the sources list is correct and up-to-date. You can check the sources list by running cat /etc/apt/sources.list.

There may be a problem with the package itself. In this case, try running apt-get install -f to fix broken dependencies and see if that resolves the issue.

If none of these suggestions helps, you may need to dig deeper to troubleshoot the problem. You can try looking at the logs for more information on what might be causing the issue. The logs for the package manager are usually located in /var/log/apt/.