An AAAA record is a type of DNS record that maps a domain name to an IPv6 address. It is similar to an A record, which maps a domain name to an IPv4 address, but it uses a 128-bit address instead of a 32-bit one. An AAAA record allows a domain name to be resolved by both IPv4 and IPv6 clients, and it is necessary for accessing websites and services that use IPv6.

Explanation
A subnet mask is a binary number that indicates which bits of an IP address belong to the network portion and which bits belong to the host portion. A slash notation (/n) indicates how many bits are used for the network portion. A /20 notation means that 20 bits are used for the network portion and 12 bits are used for the host portion. To convert /20 to a dotted decimal notation, we need to write 20 ones followed by 12 zeros in binary and then divide them into four octets separated by dots. This gives us
11111111.11111111.11110000.00000000 or 255.255.240.0 in decimal. References:
https://partners.comptia.org/docs/default-source/resources/comptia-network-n10-008-exam-objectives-(2-0),
https://www.techopedia.com/definition/950/subnet-mask

TACACS+ is a protocol that provides centralized authentication, authorization, and accounting (AAA) for network devices and users. TACACS+ can help improve the security of the management console on the company's switches by verifying the identity and credentials of the administrators, enforcing granular access policies and permissions, and logging the configuration changes made by each administrator. This way, the network administrator can ensure only authorized and authenticated users can access and modify the switch settings, and also track and correlate the changes made by each user. Reference: https://www.comptia.org/blog/what-is-tacacs