How many usable host addresses are available in a conventional IPv4 /28 subnet?
A /28 has 16 total addresses; excluding network and broadcast leaves 14 usable addresses.
How many total IPv4 addresses are contained in a /18 prefix?
A /18 leaves 14 host bits, so $2^14$ = 16384 total addresses.
How many /28 subnets can be created from one /24 IPv4 network?
The prefix increases from /24 to /28 by 4 bits, giving $2^4$ = 16 subnets.
A 1500-byte IPv4 packet has a 20-byte header and is fragmented over an MTU of 700 bytes. What is the maximum payload size of each full-sized fragment?
MTU minus the 20-byte header gives 680 bytes. 680 is divisible by 8, satisfying the fragment-offset requirement.
An IPv4 datagram has 20 bytes of header and 1480 bytes of payload. If it is fragmented into fragments carrying 500 bytes of payload each except the last, how many fragments are produced?
The payload is 1480 bytes: 500 + 500 + 480, so 3 fragments are needed.