255.255.255.224 is the correct subnet, because it gives 30 usable hosts per subnet, and will give you the most possible subnets.
A subnetwork or subnet is a logical subdivision of an IP network. The practice of dividing a network into two or more networks is called subnetting.
Computers that belong to a subnet are addressed with a common, identical, most-significant bit-group in their IP address. This results in the logical division of an IP address into two fields, a network number or routing prefix and the rest field or host identifier. The rest field is an identifier …