DRAG DROP
You are configuring a multi-subnet IPv6 network for a regional office.
The corporate network administrator allocates the 2001:0db8:1234:0800: :/54 address space for
your use.
You need to identify network IDs of the first and last subnets that you will be able to create at the
office.
Which network IDs should you identify?
To answer, drag the appropriate network IDs to the correct subnets. Each network ID may be used
once, more than once, or not at all. You may need to drag the split bar between panes or scroll to
view content.
Answer: 
Why /64?
Because /64 is the smallest subnet you can create according to IPv6 standard. IPv6 has a total of 128 Bits for an address, 64 subnet bits, 64 host bits. The question is about the first and the last network ID (=subnet) of this /54 block
your use.” From there you have to subnet which is where the /64 comes from. Your first network will always be what is assigned. Thus 2001:0db8:1234:0800: :/64 is correct. Now my subnetting of IPv6 sucks but 0bff is the highest listed, so I’m going with the answers.