"The number of available hosts on a subnet is 2h−2, where h is the number of bits used for the host portion of the address. " .......(i)
The all-zeros value and all-ones values are reserved for the network address and broadcast address respectively , thus 2 is subtracted.
"The number of available subnets is 2n, where n is the number of bits used for the network portion of the address. This is the RFC 1878 standard used by the IETF, the IEEE and COMPTIA."
here clas C means N N N H so host part have 8 bits.
3 bits are saved for subnet number . Remaining bits 8-3 = 5 bits.
according to (i) maximum number of hosts in each sub network is 25 - 2 = 32-2 = 30