"The man eats two cakes."
Translation:남자가 케이크 두 개를 먹어요.
Because "counters" exist in Korean. You add these when you are counting certain things in Korean. These are the following counters I know:
개 - for objects (thus used for "two cakes" above) 명 - for people 번 - (used when stating the number of times you did a thing e.g. twice, thrice etc.)
Sadly, Duolingo does not teach detailed grammar concepts like this.