What is the first address of a block of classless addresses

What is the first address of a block of classless addresses if one of the addresses is 192.168.2.76/10?
Network address =
First usable address =

briefly explain your answers

Solution

192.168.2.76/10

Number of bits for network address = 10

192.168.2.76 in binary representation:
   1100 0000 : 1010 1000 : 0000 0010 : 0100 100

First 10 bits will be used for Network address,
So, network address:
   1100 0000 : 1000 0000 : 0000 0000 : 0000 000

   = 192:128:0:0

So, first usable address:
   192:128:0:1