You have been provided with a Class C network $218\mathrm{.}75\mathrm{.}230\mathrm{.}0.$ Your task is to allocate IP addresses to five different networks with specific requirements:

Network $1$ requires $9$ addresses.

Network $2$ requires $28$ addresses.

Network $3$ requires $15$ addresses.

Network $4$ requires $13$ addresses.

Network $5$ requires $4$ addresses.

Each subnet must receive at least the required number of IP addresses, but it's acceptable to have unused addresses $($an equal number of IP addresses in each subnet$).$

What is the subnet mask for this case?