Why can't ubuntu install nginx and mariadb-server?

Question

Nginx

I installed ubuntu on my laptop 15.04 40 minutes ago.
I started to install everything I need, I install nginx and I get an error:

The same problem occurs when installing mariadb-server.
By the way, it also fails to remove nginx:

How to fix it and what is the cause of the problem?

Answer 1

rm /var/cache/debconf/*.dat 
apt-get clean
apt-get autoclean
apt-get autoremove
apt-get -f install

From here

Answer 2

sudo apt-get -f install
sudo apt-get install --fix-missing

Answer 3

Question one: why install 15.04 if its support will completely stop in one and a half to two months?
Set 15.10 as the latest up-to-date version.
Also, check if you connected any other crooked third-party repositories, and whether you downloaded Ubuntu from the ubuntu.com site, and it’s not clear which version it’s not clear from where?