What does it mean for a girlfriend to give her boyfriend 3.5 yuan?

A boy asked the Zen master, Master, what does 3.5 mean?

Without speaking, the Zen master took out a raw egg and a salted egg and knocked them on the boy's head respectively. He asked the boy, which egg hurts more?

Boy: Salted eggs hurt.

Zen master: If the idle egg hurts, go home and sleep. Nothing is better than numbers.