If a host on a network has the address 172.16.45.14/30, what is the subnetwork this host belongs to?

A /30, regardless of the class of address, has a 252 in the fourth octet. This means we have a block size of 4 and our subnets are 0, 4, 8, 12, 16, etc. Address 14 is obviously in the 12 subnet.