Numbers 70+

Firstly to make things better we have to separate the topic into chunks

soixante-dix
quarte-vingts
quatre-vingt-dix

Unlike the other numbers, numbers between 70-80 are different

Other than that, numbers between 80-90 are harder to comprehend

And you are wondering how to figure this out.
Here's the rule between 70-80

Here is the rule for numbers between 80-90.

This is a new one. This is the rule between 90-100.

Now we focus on the 100s.

cent
deux cents

Now we will move onto a hard number:
trois cents soixante

Au revoir