252.224.128.0/22 has addresses till 252.224.131.255. There are 2^10 hosts in the block.
It is needed that X be given 2^10/4 = 2^8 hosts. So, HID in X = 8 bits. 2 bits will be borrowed to act as SID.
So, possible subnets are:
1. 252.224.1000 0000.0/24 or 252.224.128.0/24
2. 252.224.1000 0001.0/24 or 252.224.129.0/24
3. 252.224.1000 0010.0/24 or 252.224.130.0/24
4. 252.224.1000 0011.0/24 or 252.224.131.0/24
Any one of 252.224.128.0/24 , 252.224.129.0/24, 252.224.130.0/24, 252.224.131.0/24 can be given to X.