What's the correct subnet mask ?

Hi,

I don't know if it's the good place to ask this question : I'm still a student and stuying in networking.

I had a question in an exam : What's the correct network prefix adapted on this network ?

- Router A : 172.22.0.62 with Computer A : 172.22.0.37

- Router B : 172.22.0.94 with Computer B : 172.22.0.75

And I had multiple answer : /24 ; /16 ; /20 ; /27 ; /25 ; /28.

I chose none of them but the answer if "/27".

So now I'm trying to understand why it's /27 -> 255.255.255.224. The IP is from Class B : 172.22.0.X...

Can you help me understand ?

Thanks