You can add and subtract by mathematical methods.

9 is the largest single digit. In ancient China, it was regarded as an imaginary number and extreme solar number, which often meant the most and countless meanings. In ancient China, the number 9 was a dragon. Jiuben is a snake-like animal, which highlights its triangular snake head, open Shekou and prominent snake tongue. In addition, the number nine is a snake with a human head.