I love this website because you get to see a lot more of the niche pieces of code, which can be overlooked :)

I've done a little googling around the 12000 ms timeout. It seems to be an issue with codewars not with the code. I've had a few puzzles in the past, that should of ran in milliseconds but timedout. https://github.com/Codewars/codewars.com/wiki/Error-messages:-Submission-timed-out

Also because I can't be bothered creating new projects for each puzzle on here. I just have a project called "ConsoleSandbox" on my machine. It only contains code I'm playing with, so if any of it gets deleted I'm not overly concerned.

I like the website: http://linqsamples.com

Also for learning linq you could try using linqpad. You don't need to write full programs, e.g. classes and methods, you can just write 2 lines of code and it'll work. Personally I found this site the best, as I could write code and see what everyone else was doing. If you need something quick and with intellisense you could install visual studio code. It's lightweight has intellisense to help you (and it's free)

This is a property which can be pulled through if you want it. I could of named it anything. One the where linq, if you select to name properties (in this case "index"), it will create a property which contains the current interations index. There is another property which can also be pulled through (pretty sure there are 3 properties (1: item of the list, 2: index). Anyway the second name in (n,index) is to reference the index.

Or as Visual Studio 2017 puts it:
Filters a sequence of values based on a predicate. Each element’s index is used in the logic of the predicate function.
Predicate: A function to test each source element for a condition; the second parameter of the function represents the index of the source element.

Anyway... I know both the Select and Where Linq methods allow you to pull through the index.

I have it running perfectly locally, but when I attempt it stalls on the following:

"[>*]", "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"

Instantanous locally, on your system it times out after 12 seconds.

If I alter the "Run Sample Tests" to contain the attempt stuff it runs perfectly fine. Only fails on the attempt.

I found the description on this one was very very poor. It may be because I'm not from America, but the description just says to return a number not to style it, but the test wanted symbols in the result.