SFTP uses port 22, which is the same as SSH, to ensure secure file transfers. It's important to have this port open on the firewall to allow for these secure transfers. Answer 20/21 is incorrect as these ports are used for FTP, which is less secure. Answer 80 is used for HTTP, which is not secure for file transfers. Finally, answer 443 corresponds to HTTPS, which although secure, is primarily used for secure web traffic and not specifically for file transfer protocols like SFTP.