Learn Hardcore Japanese: kaisatu de kippu wo otosite, ekiin ni tasukeraremasita. - I dropped my ticket at the gate and was helped by a station staff member.

The particle で marks the location where an action occurs. Here, 改札で means “at the ticket gate.” It tells us where you dropped your ticket.

Could you use 改札に instead of 改札で? Why or why not?

No, because に typically marks a destination or point of arrival, not the place where an action happens. If you said 改札に切符を落とした, it would sound like you aimed to drop it into the ticket gate rather than “dropped it while at the gate.”

Why is it 切符を落として and not 切符が落ちて?

落とす is a transitive verb, so the direct object (切符) takes を.
The speaker actively (even if accidentally) “dropped” the ticket.
Using 切符が落ちて would be the intransitive form (落ちる), meaning “the ticket fell” by itself, which shifts the nuance.

What does the て-form in 落として、 connect here?

The て-form links two actions in sequence.
1) 切符を落として – you dropped the ticket
2) 駅員に助けられました – you were helped by the station staff
It’s a concise way to say “I dropped my ticket and was helped.”

Why is 駅員に used before 助けられました instead of 駅員が?

In a passive sentence, the agent (the one doing the action) is marked with に. So 駅員に助けられました literally means “I was helped by the station staff.”

Why is 助けられました in the passive voice? Could this be expressed actively?

Using the passive (助けられました) emphasizes that you received help. An active version would be:
駅員が助けてくれました。
(“The station staff helped me.”)
But the passive focuses on your perspective as the one who needed and got help.

How do we know 助けられました is passive and not potential (can help)?

Potential form of 助ける is also 助けられる (“can help”), but context and particle usage clarify it.
Here, 駅員に助けられました uses に to mark the agent, so it must be passive (“was helped by”).
If it were potential, you’d expect something like 駅員を助けられました (“I was able to help the station staff”), which makes no sense here.

Who is the subject of this sentence? Why isn’t it stated?

The subject is implicitly “I” (the speaker). Japanese often omits obvious subjects when they can be inferred from context. Here, we understand it’s the speaker who dropped the ticket and was helped.