What triggers genitive case for 42 here?
"ptát se" requires an object in genitive
Ask your mother. (Ze)ptej se své matky.
I accidentally put čtyřicet and it accepted it. Are both ok?
What exactly did you put?
"Ptáme se čtyřicet dvou matek." It was where instead of typing you choose from words and I chose čtyřicet instead of čtyřiceti. I have a screenshot if it helps.
That should not be accepted and the system rejects it when I try it.