"I am haunted by the ghosts of the past."
Translation:Tôi bị ám bởi những con ma của quá khứ.
Hint says "ma" is plural, but when I tried "Tôi bị ám bởi ma của quá khứ" it said this was wrong, and suggested "Tôi bị các con ma của quá khứ ám." instead.
There are no single word in Vietnamese that is already plural like in English, so you have to say "các con ma" instead of just "ma". The suggested sentence is another way to use passive voice in Vietnamese, but your structure is also right; it's just the word that you put wrong.