CIDR Given: 196.255.128.0/18
Here you can see block size 2^14.
So for subnetting we will borrow bit from the host part.
Okk let's expand last two octate ( only last two useful for this question)
196. 255. 1000 0000 . 0000 0000
So here starting 18 bit for BID, and last 14 bit for HID.
Here Half BID wants A organization so take one bit borrow from host part.
So orgn. A= 1/2 CIDR=
196.255. 10 0 00000. 0 = 196.255.128.0/19 ( borrow 1 bit so increase group size by 1bit so 18+1 = 19)
For orgn. B= 1/4 CIDR=
196.255. 10 10 0000. 0= 196.255.160.0/20( borrow 2 bit so increase by two bit 18+2= 20)
If you still feel comfortable to understand comment .