Would it be maybe better to use a .expect("Array is empty") to handle that case for general use?

same

You can't change the order of the arguments, they always have to be a, b, c. If the arguments are 1,3,1, then 3*(1+1) would have the arguments arranged as b, a, c which is invalid.

Wow !
What a solution!

It's beyond 8 kyu I believe.
Also, some of the test are wrong as mentioned like:
1,3,1 the result is 5 while 3*(1+1)=6 ?

I Think this is a really good solution

I knew that there is a really easy way with idiomatic rust but I wanted to see if I can solve it without looking anywhere with basic syntax.

Agreed

It's not a best practice though, if there is a unwrap there is no best practice imo

Nothing wrong with any of it.

Very nice, approved ! I see you got chai working now, perhaps an update on all katas incoming once language version update has been requested ! ^^

Bad opinion.

CoffeeScript translation

Fixed.

Bad Kata and Bad Description.