The eighteenth century constitutes a distinct period in the history of Russian culture.
Восемнадцатый столетие составил периоде/о отличный на историяом и русский культура.
Explanation:
Despite the fact that "constitutes" was in present, I considered it past because 18th century is past.
"Distinct period" is accusative given that it is direct object so I ended it either with e or o.
"in the history of Russian culture" is a prepositional phrase. Hence, I ended the noun in accordance with what the grammer book instructed.Thank you very much for your help in advance.