Translation:Japan is located to the east of China.
I put "Japan is to China's east." Got it incorrect. That should be a good enough answer. Unless im missing something.
I'm not a native English speaker, but "Japan is to China's East" doesn't sound right.
It's not wrong, but it's both uncommon and more clunky than "Japan is East of China."
Maybe it needs to be "Japan is located to China's east." but I'm not sure.
Nihon wa (subject) chugoku no higashi ni (east of China) no ni denotes location in this sentence relative to Japan.
And, of course arimasu (to be, is)
Japan is east of China.
You wouldn't really say it like that in English, though people would of course understand it.
You could say "to the east of China" or just "east of China". Simply "Japan is east of China" is enough though.
Duolingo does not consequently evaluate these similar sentences in the form of "a is (located) in the ... of/to b". Its frustrating that I have to answer exactly in the way Duo thinks of.
Edit: Actually, I missed the word "the", which is likely why it was wrong.