Here subnet mask is 128 i.e. /25 is the CIDR . 1 bit is 
used 4 addressing.

Class-C address format is N.N.N.H(8bit.8bit.8bit.8bit)

for subnetting we used cisco rule

1)no of subnet= 2^1=2 ( 1 is the first on bit of last 
octate)

2)no. of host in each subnet=2^7=128-2=126( 7 is the off 
bit of last octate)

3)valid subnet=256-128=128 i.e. 0, 128

4) broadcast address= is the no. right before the next 
subnet

5) valid host= nos. between network address & broadcast 
address

below table gives u detail

subnet        0                128

1st valid     1                129
host

last valid    126              253
host

broadcast
address       127              254

but sachin as we know that ciso says that 1 st and last 
block are not used for n/w ing becose total num of n/w is 
2^n-2 so how can we use it
jitendera kuamr sinha