Remember school where I learned to write number in full text. It’s so long. Soixante dix-neuf I 79 Quatre-vingt I 80 Quatre-vingts un I 81 … Quatre-vingts treize I 93 … Cent soixante-dix neuf I 179
It’s plain math
In French part Belgium and Switzerland, they use something that make more sense like Septante | 70 Septante Un | 71 Octante I 80 Nonante I 90




Managed to find the source thanks to a post on rddit :
Ytb channel (full Japanese, no eng sub) :
Video :