"Let's not worry about those kinds of things!"
Translation:Ni ne maltrankviliĝu pri tiaj aferoj!
Why can't it be "Ne ni..."? I could find nothing online about negated imperatives.
"Ne ni maltrankviliĝu pri tiaj aferoj!" would mean something like "Not we should worry about those kinds of things", "Let others worry about it"
The negation marker is always in front of whatever it negates, be it verb, noun, pronoun, adjective or whatever.
In this example, the typical answer would be as the course indicates: "Ni ne maltrankviliĝu pri tiaj aferoj!"
Your answer, with "Ne ni..." stresses that it's not us that needs to worry about these things (implying that someone else will have to worry about them, but they're not our problem).
Why wouldn't "Ni ne zorgu pri tiaj aferoj!" mean the same -- and be several syllables shorter?