You can understand the meaning of the question like this: if you have a son, the money for your son and wife is1:2; If she gives birth to a daughter, the money for the daughter and wife is 2: 1. So the money of three people is the son: wife: daughter = 1:2:4, so the son gets one seventh, the wife gets two sevenths and the daughter gets four sevenths.

This is based on my personal opinion, I hope I can help you!