Answer:
3
Step-by-step explanation:
The answer is within the question.... since it talks about triangulation.... a triangle.
The principle is that from each station, you get a distance location from that station of the event. Then from each center you make a circle with the distance measured at that center.
All three circles done form the monitoring centers will meet at a point somewhere between those three centers, and you'll get your location.
That's the triangulation process. You do need 3 points for a precise reference, if you have only 2, you are left with 2 possibilities.