this should be a 8kuy kata.

Math everywhere: linear equation

It's in the title.

It's not a 3 kyu task, and it's not intended to be.

How is this kata a 6kuy? This is too easy.

My initial solution in Python is a bruteforce, and it passed. So you don't even need to be as smart as the user above to be able to solve this kata.

If you're at 2 Dan with 3000 Katas solved, I'm sure.

But this is marked 7 kyu, which is absurd.

Saying that this kata is simple is rather a misnomer. Definitely not a 7kyu.
Might be easy for you if you remember a very specific math lesson from school.
Otherwise there is no chance to deduce the solution.

This thing is definitely not 7kyu.

What was the point of this kata?

wow - this is the most pointless kata - really got annoyed with it.

Please use spoiler flag next time.

Just bad kata - why would you put null as param and expect -1;