Interesting. Your launches work. Sort of. You just need to specify if you want the classic notebook interface, if that is what you indeed prefer? A few months ago the default switched to JupyterLab, see here and here and here.
You can link to the classic notebook dashboard/tree interface successfully by changing the code for your launch badge for the first repo you posted to this:
[](https://mybinder.org/v2/gh/yajuna/tmath307/master?urlpath=/tree/)
For the second one, the launch link would be similar at the end, specifying the repo in the earlier part:
https://mybinder.org/v2/gh/yajuna/tmath308summer19/master?urlpath=/tree/
You are seeing the 404 error because JupyterLab isn’t working for you. That is odd. I suspect because you have runtime.txt there limiting Python to an old version? (Just a guess because I haven’t seen this yet.) Do you need the old version? If you do and you don’t care about JupyterLab, I think you’ll be okay with just fixing your launch link to specify the classic notebook interface.
From the 404 error page you are seeing presently, if you just changed the end of the URL in your browser from reading /lab to reading /tree you would have switched interfaces in the already running session. It is handy trick to know about that when troubleshooting things like you were encountering that prompted your post.