Learn Farsi: این ماشین چهار مسافر دارد.

In Farsi, whenever you use a number or a quantity word like چند (how many), the noun that follows it must be singular. So, instead of saying "four passengers" like in English, Farsi literally says "four passenger" (چهار مسافر).

If I wanted to ask "How many passengers does this car have?", how would I change this sentence?

You would simply replace the number چهار (four) with the question word چند (how many). The sentence becomes: این ماشین چند مسافر دارد؟ Just like with the number four, the noun مسافر stays singular after چند.

Why is the verb دارد (has) at the very end of the sentence?

Farsi sentences typically follow a Subject-Object-Verb word order. این ماشین (this car) is the subject, چهار مسافر (four passengers) is the object, so the verb دارد (has) is placed at the end.

Does the verb دارد agree with the car or the passengers?

The verb always agrees with the subject of the sentence. Here, the subject is این ماشین (this car), which is a single thing (third-person singular). Therefore, we use دارد (has), even though the object involves multiple people.