And if you want some information on how you'd know:
"Passed" is always a verb ("I passed the car" "he passed away").
Past can be a noun ("I knew him in the past") and adverb ("he drove past me"), and adjective ("the past events were a success") or as a preposition ("the high school is down the road just past the convenience store"). But not a verb.
In your sentence, "passed" is used as a preposition. Which means it should be "past."
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