its a subnet of class B . so 16 net 16 host id .
255.255.31.0 =
255.255. 00011111.00000000 there are 8+3 = 11 0`s 21 1`s
so no. of subnet possible 2^(21-16 ) = 32
Supernet means combination of two or more networks (or subnets) with a common Classless Inter-Domain Routing (CIDR) . So max supernet subnet mask for this will be Class b subnet mask . 255.255.0.0 .