Unable to install libsdl2-dev due to unmet dependencies

Don't try this command:

sudo apt-get install 229-4ubuntu6

E: Unable to locate package 229-4ubuntu6

Because there isn't any package with 229-4ubuntu6 name in repositories.

The apt output says

libudev1 (= 229-4ubuntu4) but 229-4ubuntu6 is to be installed

That means , the 229-4ubuntu6 version of libudev1 has been installed yet but the 229-4ubuntu4 version is required.

And the other things is that, the last version of libudev1 for xenial is 229-4ubuntu17 but your apt returns the last version is 229-4ubuntu6. This issue is happened because of that, many Ubuntu's repositories is disabled on your system and your repositories is not updated.

So as the first step we try to enable all of your Ubuntu repositories with this commands:

sudo add-apt-repository main
sudo add-apt-repository universe
sudo add-apt-repository restricted
sudo add-apt-repository multiverse

Then update your repositories and your packages:

sudo apt update
sudo apt upgrade

Then try to fix broken packages:

sudo apt -f install

And as the last step try to install libsdl2-dev package:

sudo apt install libsdl2-dev

Update: Please add this lines to your /etc/apt/sources.list file:

deb http://archive.ubuntu.com/ubuntu xenial universe multiverse
deb-src http://archive.ubuntu.com/ubuntu xenial universe multiverse

deb http://us.archive.ubuntu.com/ubuntu/ xenial universe
deb-src http://us.archive.ubuntu.com/ubuntu/ xenial universe
deb http://us.archive.ubuntu.com/ubuntu/ xenial-updates universe
deb-src http://us.archive.ubuntu.com/ubuntu/ xenial-updates universe

deb http://us.archive.ubuntu.com/ubuntu/ xenial multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ xenial multiverse
deb http://us.archive.ubuntu.com/ubuntu/ xenial-updates multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ xenial-updates multiverse

deb http://security.ubuntu.com/ubuntu xenial-security universe
deb-src http://security.ubuntu.com/ubuntu xenial-security universe
deb http://security.ubuntu.com/ubuntu xenial-security multiverse
deb-src http://security.ubuntu.com/ubuntu xenial-security multiverse

And comment this lines:

deb http://ftp.belnet.be/ubuntu.com/ubuntu/ xenial multiverse restricted universe main
deb-src http://ftp.belnet.be/ubuntu.com/ubuntu/ xenial multiverse restricted universe main #Added by software-properties

And then try this commands to update repositories and packages:

sudo apt update
sudo apt upgrade

Then try to install it again:

sudo apt install libsdl2-dev