Errand Chronicle 31011 · Entry #4

Pyresh's Formula IV

Objective
Found a trace of Pyresh. Let's solve Pyresh's Formula written on it.
Solve the secret formula left behind by Pyresh and type it in the chat window;
Dialogue
Trace of Pyresh Dialogue
Pyresh left behind a piece of his realizations.
Numbers are written in what looks to be a riddle of sorts.
After a sequence of numbers follows a question mark.
It's as if someone wanted their formula to be solved by another.
57 - 410 = 27
48 - 322 = 17
21 - 121 = ?
Trace of Pyresh Dialogue (Alt)
57 - 410 = 27
48 - 322 = 17
21 - 121 = ?
Trace of Pyresh Completion
The riddle-like numbers here
stand for dates of the calendar.
The number of days between
February 1 and January 21 are 11!
You feel your head's about to burst with pain,
but you've solved Pyresh's Formula.
Other Errands in This Chronicle

9 further errands share this chronicle — the same travelers, the same stretch of road.

Details
Chronicle31011
Entry4
Quest Giver
Turn-in
Summary
The riddle-like numbers here
stand for dates of the calendar.
The number of days between
February 1 and January 21 are 11!
You feel your head's about to burst with pain,
but you've solved Pyresh's Formula.