You get some kind of prototype laser weapon, which Janey points out, so she wants you to test it out on some Scavs. You will need to kill a total of 15 Scavs with that laser weapon equipped. When you get to one of the locations and begin killing Scavs, Janey will chime in and set an optional objective for you.

This optional objective is to ignite a total of 5 Scavs, which she points out is best in an oxygen-rich environment. That means that you need to go inside the buildings and lure the Scavs into them, then shoot at them with the laser and hopefully set them ablaze. It appears the enemy has to die from the fire Damage over Time in order for it to count for the optional objective.

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Remember that there’s more Scavs than indicated on the map, including the Darksiders camp (right). Also, in order to ignite enemies, you will need to shoot them in an oxygen-rich environment.

An easier way to finish the optional objective is to fire the weapon at the Scavs inside a building with oxygen (or using one of the oxygen dispensers) and if the enemy doesn’t catch fire close to death, kill that enemy with another weapon. If you run out of enemies to kill at all three locations, save and quit, then try again. Once you fill your quota, go to Janey in Concordia to finish the mission.