For a WAN link you would use 255.255.255.252, which would give you for example 203.8.7.248 for a subnet address and 203.8.7.249 and 203.8.7.250 for each end and 203.8.7.251 as the broadcast address. The next subnet would be 203.8.7.252.

To calculate the number of address in a subnet mask you would subtract the final byte from 255 and add 1, ie 255 - 252 + 1 = 4 which is the number of address for that subnet mask. The reason for adding one is because the numbering range is 0 to 255 which actually gives you 256, hence the add 1. This works for all masks to. Then you get to reverse bit masking too. I have been meaning to write some simple rules to help with this but have been quite busy.