Given, the site address as 181.56.0.0.and the company needs 1000 subnets means we need to borrow atleast 10 bits from 3rd and 4th octect i.e;
181.56.11111111.11 000000 (1's represent the total subnets needed and remaining 0's are hosts)
so subnet mask is 181.56.255.192
now,
the first subnet will contain all 0's and it will be our subnet id...i.e;
181.56.00000000.00 00000000 $\rightarrow$ 181.56.0.0
and DBA of first subnet is 181.56.0.63 i.e; 181.56.00000000.00 111111