Madame, restez calme, nous bientot arriverons , Can you not use the future instead of always aller and the infinitive. ?
You never put the adverb between the subject and the verb: « nous arriverons bientôt » is correct & accepted! :)
I did that and still got wrong, because the hint says stay calm is called guarde ton calme.
"Gardez votre calme" should be accepted.
Why not "reste calme"?
That would be the « tu » version which you would never use with someone you address as « Madame » ! In other circumstances, you would be correct! :)
Can we say 'calmez-vous'?
That would mean "Calm down!" which a somewhat different register to the above! :)
what's wrong with madame, restez vous calme?
Restez-vous calme means "Are you staying calm?", not "Stay calm"