Functional Programming Exercise: Refactoring

Functional Programming Exercise: Refactoring
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Hello, I am stuck with this particular exercise, and I need better explanation. Here is the link

https://learn.freecodecamp.org/javascript-algorithms-and-data-structures/functional-programming/refactor-global-variables-out-of-functions

What part are you stuck on or confused by? What have you tried? What tests are failing?