The given block of addresses is 131.210.16.0/21. To create four subnets with equal number of IP addresses, we need to borrow 2 bits from the host portion to create 4 subnets, which gives us a block size of 2^2 = 4.
i. The prefix for the original block of addresses is 131.210.16.0/21. To create 4 subnets, we need to borrow 2 bits from the host portion, so the new prefix length will be 21 + 2 = 23. The block size for each subnet will be 2^2 = 4, so the new subnet masks will be:
Subnet 1: 131.210.16.0/23 Subnet 2: 131.210.18.0/23 Subnet 3: 131.210.20.0/23 Subnet 4: 131.210.22.0/23
ii. The original block of addresses has 2^(32-21) = 2^11 = 2048 IP addresses. Since we are creating 4 subnets, each subnet will have 2048/4 = 512 IP addresses. However, 2 IP addresses from each subnet are reserved for the network address and the broadcast address, so the number of host addresses that can be supported per subnet is 512 - 2 = 510.