How can I fix these errors please ?
~$ sudo add-apt-repository ppa:mktcoin/mktcoin
[sudo] password for jax:
Cannot add PPA: 'ppa:~mktcoin/ubuntu/mktcoin'.
ERROR: '~mktcoin' user or team does not exist.
sudo apt-get install libdb4.8-dev libdb4.8++-dev
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package libdb4.8++-dev is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
Package libdb4.8-dev is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package 'libdb4.8-dev' has no installation candidate
E: Package 'libdb4.8++-dev' has no installation candidate
Ubuntu and Debian have their own libdb-dev and libdb++-dev packages, but these will install BerkeleyDB 5.1 or later, which break binary wallet compatibility with the distributed executables which are based on BerkeleyDB 4.8. If you do not care about wallet compatibility, pass --with-incompatible-bdb to configure.
apt-get install libdb-dev libdb++-dev
./configure --with-incompatible-bdb