How do i solve unmet dependencies for a package?

Question

I have a red stop sign in my toolbar; it reads as follows:

An error has occurred. Run package manager from the right click menu or apt-get in a terminal to see what is wrong. The error message was: "error. brokencount > 0 this usually means you have unmet dependencies."

I tried to solve the problem with:

 sudo apt-get install -f

I got this message:

Reading package lists... Done
Building dependency tree       
Reading state information... Done
Correcting dependencies... Done
The following extra packages will be installed:
libmysqlclient18
The following packages will be upgraded:
libmysqlclient18
1 upgraded, 0 newly installed, 0 to remove and 572 not upgraded.
3 not fully installed or removed.
Need to get 0 B/2.892 B of archives.
After this operation, 3.471 kB disk space will be freed.
Do you want to continue? [Y/n] y
dpkg: error processing archive /var/cache/apt/archives/libmysqlclient18_10.1.18+maria-1~trusty_amd64.deb (--unpack):
libmysqlclient18:amd64 10.1.18+maria-1~trusty (Multi-Arch: no) is not co-installable with libmysqlclient18 which has multiple installed instances
E: Sub-process /usr/bin/dpkg returned an error code (1)

Solution

Open terminal and type

  sudo dpkg --configure -a

If it doesn't help then do this

  sudo apt autoremove <packagename>

If this doesn't help then you Need an internet connection.Type in terminal

  sudo apt-get autoclean

remove sources.list file.and create new sources.list...

sudo rm /etc/apt/sources.list 

Then, type in

sudo software-properties-gtk 

This will open software-properties-gtk and a newsources.list will be created automatically.

Then change the server to US or to any other server of your choice. You must enable repositories from the new dialog in order to create new sources.list.

Tick all the boxes then click on Revert then click close.

Need to restore default repositories

 sudo apt-get update && sudo apt-get dist-upgrade -y

(it is good practice to backup this file before installing to recover if such things happen)

Now install anything!

 sudo apt-get install mysql-server