
Quoting
pg1067
This question makes little sense as phrased.
You used the word "it" twice, but it's unclear what the antecedent of that pronoun is. You wrote that "a camera flashed for [a] red light" and that you were "supposed to respond to it." As phrased, "it" must refer either to the camera or the red light (those being the only two nouns in the sentence to that point), but responding to a camera or a red light makes no sense. You then said something about getting another letter, which implies that you received a letter. If you're saying that you received a letter regarding the red light, I would hope it obvious that you should reply to that letter within the time stated in the letter.
If you want to clarify what you're talking about, we can try to provide more information. Note, by the way, that you should identify the city where this occurred because these things are not handled the same everywhere.