Tady to máš vyřešené (samozřejmě jen a pouze pro tvoji kontrolu)

Address:   172.18.3.0           10101100.00010010.00000011. 00000000
Netmask:   255.255.255.0 = 24   11111111.11111111.11111111. 00000000
Wildcard:  0.0.0.255            00000000.00000000.00000000. 11111111
=>
Network:   172.18.3.0/24        10101100.00010010.00000011. 00000000
HostMin:   172.18.3.1           10101100.00010010.00000011. 00000001
HostMax:   172.18.3.254         10101100.00010010.00000011. 11111110
Broadcast: 172.18.3.255         10101100.00010010.00000011. 11111111
Hosts/Net: 254                   Class B, Private Internet

1. Requested size: 30 hosts
Netmask:   255.255.255.224 = 27 11111111.11111111.11111111.111 00000
Network:   172.18.3.0/27        10101100.00010010.00000011.000 00000
HostMin:   172.18.3.1           10101100.00010010.00000011.000 00001
HostMax:   172.18.3.30          10101100.00010010.00000011.000 11110
Broadcast: 172.18.3.31          10101100.00010010.00000011.000 11111
Hosts/Net: 30                    Class B, Private Internet

2. Requested size: 10 hosts
Netmask:   255.255.255.240 = 28 11111111.11111111.11111111.1111 0000
Network:   172.18.3.32/28       10101100.00010010.00000011.0010 0000
HostMin:   172.18.3.33          10101100.00010010.00000011.0010 0001
HostMax:   172.18.3.46          10101100.00010010.00000011.0010 1110
Broadcast: 172.18.3.47          10101100.00010010.00000011.0010 1111
Hosts/Net: 14                    Class B, Private Internet

3. Requested size: 10 hosts
Netmask:   255.255.255.240 = 28 11111111.11111111.11111111.1111 0000
Network:   172.18.3.48/28       10101100.00010010.00000011.0011 0000
HostMin:   172.18.3.49          10101100.00010010.00000011.0011 0001
HostMax:   172.18.3.62          10101100.00010010.00000011.0011 1110
Broadcast: 172.18.3.63          10101100.00010010.00000011.0011 1111
Hosts/Net: 14                    Class B, Private Internet

Needed size:  64 addresses.
Used network: 172.18.3.0/26
Unused:
172.18.3.64/26
172.18.3.128/25