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While Sofia thinks some more about the situation with Emerson Hale, there is another robot to destroy.
Head to the New Appalachian Central Trainyard and kill the U.S.S.A. Protectron. Optionally loot the algorithm update from the bot's remains. Watch out for the feral ghouls that are normally meandering around the yard while finding the Protectron. After that, return to Sofia to complete the quest.
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