is economics a part of humanities?

Economics is considered a "social science". Hence the reason it is listed under "social science" in Yahoo Answers.

No. The humanities answer the same questions as the social sciences, but through analytic reasoning and not through empirical methods. The empirical study of language for example is linguistics, however the humanities also study language as a discipline, but without using empiricism. The approximate equivalent to economics in the humanities is philosophy. Economics is the study of how people make choices when their choices are constrained, subject to empirical measurement.

Economics Humanities