Translation:The park is located in the city's east side.
“Located” is not necessary for this sentence and there isn't a Chinese word here that means located. I don't see why that word appears in the translation at all. “The park is in the city's east side” translates 在 to “is in.” I think the answer with “located” in it should be marked as wrong.
Reported on February 12, 2019: "The park is located on the east side of the city."
It appears that for this particular skill, for many of the Chinese sentences Duolingo only accepts only one translation, this one included. Lots of work is needed in order to fix this issue.