Lemme try this.

If Vlan 40 includes 192.168.1.0 and 192.168.2.0 then the mask for the VLAN will be /23 or 255.255.254.0.

512 addresses - 2 (network address of 192.168.1.0 and broadcast address of 192.168.2.255)

Supernets are used in large enterprise networks with large switch fabrics. I see them everyday.

hth

catman