How old is the girl in the old calendar book, and in which month did she conceive the girl?

7749 (base 49)

Ask mom when she has it (plus the lunar calendar of pregnancy)

Excluding the mother's birth (minus the actual age of pregnancy)

Plus 19 (the last single number is male, and the double number is female)

Take someone as an example: 1985 was born, last menstrual period 12.9.27, pregnant in August of the lunar calendar, and pregnant at the age of 27. The formula is: 49+8-27+ 19=49, which is singular, boy.