It is not imperative to always start with the largest network but it is easier if you're not accustomed with sub-netting.
You can take it this way:
10.97.21.0/24 network into 2 /25 networks:
Since you need a /25, keep one and further subnet the other one, once again in two networks:
You need a /26, so you keep the first one and divide the other one in two:
as you can see we get the solution given by @Datagram.Network, but if choose instead to divide the first subnet and keep the second we can also have
For more information you may find this answer to How do you calculate the prefix, network, subnet, and host numbers? interesting