Hi Itai,
It’s probably best to stick to use “A” instead of “10” as it can be confusing. It’s easy to read it as 10 while in reality it’s one, zero.
About the subnets…the ISP will give you a /48 global prefix that you can use for your network. You should use /64 subnets since it’s convenient for autoconfiguration which leaves you with 16 bits you can use to create different subnets.
A typical exam question could be something like:
“The ISP has given you global prefix 2001:41f0:4060::/48. You have five VLANs that require connectivity. What subnets will you use? Also, for each subnet what IPv6 address will you assign to your default gateway?”
Rene