Find the three numbers to the safe code

The  task is a freeplay storyline mission featured in S.T.A.L.K.E.R.: Lost Alpha.

"Blue Silhouette, if you are reading this, the zone has taken me. It is up to you to get back to our hiding place and take care of the stash. I changed the combination lock on the door, but I remember how much you like puzzles, so I updated the PDA's GPS tracker to play an audio message once you get close to 3 areas."

- PDA message history

Overview

 * The mission is listed in the gamefiles as a storyline mission and appears during Freeplay.
 * Taking the Red Fox's PDA from the rookie corpse near Rookie Village spawns the mission.
 * There are three objective locations couched as riddles that need to be visited sequentially in order to obtain a three digit code.
 * completion spawns the Find the safe storyline mission.