IPV4 Network Planning

Hello,

I have to deploy 4 subnets using 129.108.10.0/21

The subnets are as follows:

Subnet A: 280 computers
Subnet B: 130 computers
Subnet C: 75 computers
Subnet D: 20 computers

I did the calculations but I need verification the following is correct and
why:

Subnet A: 129.108.10.0/22
Subnet B: 129.108.10.0/23
Subnet C: 129.108.10.0/24
Subnet D: 129.108.10.128/26

Could someone please help me?

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Thank you for your help!
JYC