Why is it tetrahedral?

This is an A-level exam question but its from a specimen paper.

Maybe I’m being really dense but I’m just confused why [RhCl4]2- is tetrahedral and not square planar.

My workings are at the bottom of the page and I’ve attached the full question.

Also if anyone knows why the answer is what it is for the second question, that wouod be greatly appreciated 😭😭🫶.