Questions & Answers about Mój szef jest bardzo dumny z tego eksportu.
Why do we use the preposition z here to mean "of"?
The adjective dumny (proud) always governs the preposition z followed by the Genitive case. While English uses "proud of", Polish uses dumny z. When you learn adjectives like this, you have to memorize the specific preposition and case they demand.
Why does the masculine noun eksport end in -u (eksportu) rather than -a in the Genitive case?
Masculine inanimate nouns in the Genitive singular take either an -a or -u ending. The -u ending is typically used for abstract concepts, uncountable nouns, and many borrowed foreign words. Because eksport is both an abstract business concept and a loanword, it takes -u.
If I wanted to say the boss is proud of the action of "exporting", how would this change?
You would need to replace the regular noun eksport with the verbal noun (gerund) for exporting, which is eksportowanie. Because dumny z still requires the Genitive case, the phrase would become dumny z eksportowania.
Since it follows the verb jest (is), why isn't the adjective dumny in the Instrumental case?