After some googling we can understand that we can work with ISO files. You can extract the whole system into your machine.
For that I booted up a Kali Linux virtual machine, and used the following command to mount our iso file.
sudo mount -o loop iso_file_name.iso tmp
At this point I got stuck again, and really I had no background about files like this and I have never extracted an iso file before.
But luckily we have google. After searching about the files we mounted. I find out that there's a file named filesystem.squashfs, and if you extract it you will have the actual files in the system.
Using the following command I was able to extract everything in the casper directory.
sudo unsquashfs -f -d /home/kali/Desktop/tmp /home/kali/Downloads/tmp/file.squashfs
Let's see what we got on that ~/Desktop/tmp directory.
Now we have all the actual files that are in the system.
We can enumerate as we want. See files like /etc/shadow etc...
If we look at the root home directory and look for something in .bash_history. We will find the password for zaz user.
And now we can continue our explotation with the writeup4.md to get root.
You can see now after viming into .bash_history we have zaz's password
adduser zaz
646da671ca01bb5d84dbb5fb2238dc8e