Untitled

bengisu@bengisu-VirtualBox:~/Desktop$ sudo apt update
[sudo] password for bengisu: 
Get:1 http://security.ubuntu.com/ubuntu focal-security InRelease [114 kB]
Get:2 http://security.ubuntu.com/ubuntu focal-security/main amd64 DEP-11 Metadata [35,8 kB]
Get:3 http://security.ubuntu.com/ubuntu focal-security/universe amd64 DEP-11 Metadata [64,7 kB]
Get:4 http://security.ubuntu.com/ubuntu focal-security/multiverse amd64 DEP-11 Metadata [2.464 B]
Err:5 http://tr.archive.ubuntu.com/ubuntu focal InRelease                      
  Temporary failure resolving 'tr.archive.ubuntu.com'
Err:6 http://tr.archive.ubuntu.com/ubuntu focal-updates InRelease              
  Temporary failure resolving 'tr.archive.ubuntu.com'
Err:7 http://tr.archive.ubuntu.com/ubuntu focal-backports InRelease
  Temporary failure resolving 'tr.archive.ubuntu.com'
Fetched 217 kB in 30s (7.175 B/s)       
Reading package lists... Done
Building dependency tree       
Reading state information... Done
All packages are up to date.
W: Failed to fetch http://tr.archive.ubuntu.com/ubuntu/dists/focal/InRelease  Temporary failure resolving 'tr.archive.ubuntu.com'
W: Failed to fetch http://tr.archive.ubuntu.com/ubuntu/dists/focal-updates/InRelease  Temporary failure resolving 'tr.archive.ubuntu.com'
W: Failed to fetch http://tr.archive.ubuntu.com/ubuntu/dists/focal-backports/InRelease  Temporary failure resolving 'tr.archive.ubuntu.com'
W: Some index files failed to download. They have been ignored, or old ones used instead.
bengisu@bengisu-VirtualBox:~/Desktop$ sudo apt install build-essential
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package build-essential 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 'build-essential' has no installation candidate
bengisu@bengisu-VirtualBox:~/Desktop$ sudo apt install gcc
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package gcc 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
However the following packages replace it:
  gcc-9-doc gcc-10-doc

E: Package 'gcc' has no installation candidate
bengisu@bengisu-VirtualBox:~/Desktop$