We really frown on answering homework questions here. However, I will help point you in the right direction.
ls -la /bin/passwd outputs:
-rws--x--x 1 root root 29992 Nov 7 08:29 /bin/passwd
The key here are the permissions "-rws--x--x" and the owner of the file "root". So lookup the linux permission model and it'll answer your question. Keep in mine the s in rws is not a typo.
I'd recommend reading the man page for chmod. In general, always start your research with the man pages...