Which of the following default port numbers need to be open on a firewall for a mail server to successfully send and receive mail? (Choose three.)

What data communication protocol uses characters or "handshaking" to control the link and represent information?

a. Asynchronous protocol. b. Binary synchronous protocol. c. Synchronous Data Link Control (SDLC). d. High-Level Data Link Control (HDLC).

If X = 6 and Y = 2, what is the value of the following expression:

4 + ( 3 ^ Y ) * ( X + 2 ) / Y a. 59 b. 40 c. 52 d. 26