"Het restaurant heeft een grote en een kleine keuken."
Translation:The restaurant has a big and a small kitchen.
In future if you are unsure you might want to look it up in an online dictionary. It's not perfect but Wiktionary (a dictionary/thesaurus sister site of Wikipedia) is generally a good starting point. The entry for keuken is here. You should see that it is listed as keuken f. The f tells you that it is feminine. Both masculine and feminine words are "de" words, while "het" words are neuter. (You should notice therefore that de is equivalent to German der and die, while het is equivalent to das).