I know there are bunch of references on stackoverflow or other resources, but I couldn't find any applicable solution.
Followings are some of the solution I tried.
sudo apt update
sudo apt-get install gcc-4.5
sudo apt install gcc-4.5
gives error E: Package 'gcc-4.5' has no installation candidate
deb http://dk.archive.ubuntu.com/ubuntu/ xenial main
gives error
E: The repository 'http://dk.archive.ubuntu.com/ubuntu xenial InRelease' is not signed.
sudo apt install software-properties-common
sudo add-apt-repository ppa:ubuntu-toolchain-r/test
gives error E: The repository 'http://ppa.launchpad.net/jonathonf/gcc/ubuntu kinetic Release' does not have a Release file.
I'm really stuck on this simple problem for a few days. Thanks for your help.