Die Zusatzkosten entstanden durch den Anschlussverlust.

Because Zusatzkosten is the subject of the sentence, so it is in the nominative case, and it is plural.

• die = nominative plural article
• Zusatzkosten = extra/additional costs

So die Zusatzkosten means the additional costs or the extra costs.

A useful thing to notice is that German often uses Kosten in the plural when English might also think in terms of costs rather than one single fee or charge.

Because German very often forms compound nouns by joining words together.

Here:

• Zusatz = addition, extra
• Kosten = costs

So Zusatzkosten literally means additional costs.

German strongly prefers this kind of compound spelling. Writing Zusatz Kosten as two separate words would be wrong.

You could also say zusätzliche Kosten, and that would be correct too. The difference is:

• Zusatzkosten sounds a bit more compact, technical, or administrative
• zusätzliche Kosten sounds a bit more like a normal adjective + noun combination

It is the verb entstehen, in the simple past (Präteritum), agreeing with a plural subject.

The forms are:

• infinitive: entstehen
• simple past singular: entstand
• simple past plural: entstanden
• past participle: entstanden

That means entstanden can look confusing, because the simple past plural and the past participle have the same form.

In this sentence, it is the finite verb in a main clause, so it is simple past, not a participle.

Because there is no auxiliary verb such as sein.

Compare:

• Die Zusatzkosten entstanden durch den Anschlussverlust.
  = simple past

• Die Zusatzkosten sind durch den Anschlussverlust entstanden.
  = present perfect

In the sentence you were given, entstanden is in the normal verb position of a main clause, so it is functioning as the main finite verb.

Yes, that is a very good way to think about it.

entstehen often means:

• to arise
• to come about
• to occur
• to be caused / to result

With things like costs, problems, or damage, German often uses entstehen where English might use several different verbs depending on style.

So Zusatzkosten entstanden is a natural German way to say that extra costs arose or were incurred.

No. It is not passive.

The sentence is grammatically active, but the verb entstehen is intransitive, so it does not take a direct object.

That is why it feels different from English. English might prefer something like:

• the extra costs were caused by ...
• the extra costs resulted from ...

German often uses entstehen instead of a passive construction like wurden verursacht.

So:

• Die Zusatzkosten entstanden durch den Anschlussverlust. = active
• Die Zusatzkosten wurden durch den Anschlussverlust verursacht. = passive

Both are possible, but the first is very natural.

Because durch always takes the accusative case.

So:

• nominative: der Anschlussverlust
• accusative: den Anschlussverlust

That is why the sentence has durch den Anschlussverlust.

This is one of the prepositions that learners usually memorize with a fixed case:

• durch
  • accusative
• für
  • accusative
• gegen
  • accusative
• ohne
  • accusative
• um
  • accusative

In German compound nouns, the last element determines the gender.

Here the last part is Verlust:

• der Verlust = loss

So the whole compound is also masculine:

• der Anschlussverlust

This is a very useful rule for compounds. For example:

• das Haus → das Wohnhaus
• die Bahn → die Straßenbahn
• der Verlust → der Anschlussverlust

It is made from:

• Anschluss
• Verlust

The final part, Verlust, gives the basic category: it is some kind of loss.

The first part, Anschluss-, tells you what kind of loss it is.

This is how many German compounds work:

• the last element gives the main meaning
• the earlier element(s) narrow it down

So Anschlussverlust is literally a loss of connection/transfer/continuity, depending on context.

Yes. German main clauses allow some movement, but the finite verb must stay in second position.

You could also say:

• Durch den Anschlussverlust entstanden die Zusatzkosten.

That version puts more emphasis on the cause.

Both are correct. The difference is mostly about focus and style, not basic meaning.

It is natural German, but it sounds a bit formal, written, or administrative.

You might see it in:

• a report
• a complaint
• customer-service correspondence
• a technical explanation

In everyday speech, people might more often say:

• Die Zusatzkosten sind durch den Anschlussverlust entstanden.
• Wegen des Anschlussverlusts sind Zusatzkosten entstanden.

So the original sentence is perfectly normal, just a little more formal in tone.

Because they are nouns, and in German all nouns are capitalized.

That includes:

• simple nouns: Kosten
• compound nouns: Zusatzkosten, Anschlussverlust

This is one of the most visible spelling rules in German and helps readers recognize nouns quickly.