Question

1. Explanation of what “chmod 753 filename” does.

Answer 1

command "chmod 753 filename" means 
This changes the file permissions of user, group and others to 753

3 bit binary represents rwx permissions
Where r is read, w is write and x is execute

7 in binary is 111
This belongs to user.
So, users can read, write and execute file  

5 in binary is 101
This belongs to group
So, group can read and execute file 

3 in binary is 011 
This belongs to others
So, users can write and execute file