It doesn't seem an unreasonable assumption that the 11.4% has been calculated on the same basis as the 15%
The mistake in the question as posed would appear to be, either 11.4% should have read 11.4kg (in which case I still have an issue with 1.89 being rounded to 1.8) or 1.8kg is wildly wrong and the answer should 3.23kg.
Go here for actual practice and note the warning at the end which cautions against adding water directly to grain and not seeking to increase content by this method by more than 2%!!
http://www.ag.ndsu.ed...tsci/crops/ae905w.htm