I think this is an accidental kata. Otherwise, please make a description more informative.

Really needs a fixed input to build around

Ok, let's try to put it nicely: welcome as a fellow codewarrior and we all hope that you will joing us for good and for a long while on this training ground.

As this is indeed a training ground, we are allowed to contribute creating our own kata. Incidentally creating katas proves to be a great source of experience as we have to build tests to work on code we often cannot even imagine and we get to read about other people's wit and creativity.

Wit and creativity are missing here, as it is all about writing a variable assignment, one of the most basic, plain and flat concepts you can learn in your first hours (if not minutes) as a beginner.

I invite you thus to refactor this kata a bit, trying to had some of the spice we all around here crave for: challenge :)

This seems a tad bit too easy, even for a 8 kyu level.
How about making it a bit more interesting by adding a constraint, such as "no equal sign allowed in the code" and/or "don't use the number 4"?

a could also equal 3.