If you are facing the issue, Could not resolve 'archive.ubuntu.com', you can fix them manually by appending a couple of lines in one of the files in Ubuntu. I have set up Ubuntu in Virtual Box and whenever I tried to install anything from ppa, I was getting this error of "Could not resolve archive.ubuntu.com".
You can fix this problem by changing a DNS address manually into the file /etc/resolv.conf to the free DNS entry provided by Google.
Before you follow the steps, sudo as a root user, and do not forget to back up your existing file.
Navigate to /run/resolvconf.
Edit the file resolv.conf via vi resolv.conf and add this two lines in the starting of the file.
Next time you wont face the problem of "Could not resolve archive.ubuntu.com".