In the ES6 part, there is mention of apply, reduce and filter, but I don’t remember them being taught in any of the earlier modules. I think it would be better if coding concepts that feature in a challenge were taught before the challenge, so that we already know what they are. It is also a bit confusing using those terms in the challenges when they are not required in the coding answer.
It is a thing brought up often, ES6 syntax is important but the challenges use things taught in future lessons. There will be a new version of this challenge soon, hopefully it will makes things clearer