Depends on the encryption algorithm. If it's something outdated like MD5, sure. If they used something like AES-256 with a proper-sized (>1024b) key, it wouldn't be worth the effort.
Depends on the salt they used and the number of rounds of AES they used.
If they didn't salt their hashes then it's easy to make a rainbow table of well known passwords and match them to users, regardless of hashing algorithm.
Depends on the encryption algorithm. If it's something outdated like MD5, sure. If they used something like AES-256 with a proper-sized (>1024b) key, it wouldn't be worth the effort.
Depends on the salt they used and the number of rounds of AES they used.
If they didn't salt their hashes then it's easy to make a rainbow table of well known passwords and match them to users, regardless of hashing algorithm.