Translation:You are rich because of my rent, sir.
Apparently, according to Wiktionary, "أُسْتاذ" is actually borrowed from Persian, the word being "استاد" (ostad), which means "skilled person," "master," "expert," or "craftsman." It has gone on to be borrowed in many languages in addition to Arabic, including Hindustani (उस्ताद), Malay (ustaz), and Turkish (usta).
Even so: in English English, "sir" hasn't been used in that way for about a hundred years. (American English is different). I wish the English translations could be more idiomatic: it means that, when you are trying to find an English translation, you have to really think hard about what awful obsolete phrasing duolingo might be expecting.