If I have taken U.S. History 1 and 2 and World History. Would that be 3 years of history or 3 years of social studies?
It’s however you want to report it. History is usually considered part of social studies. In many schools, APHG and Economics are part of the Social Studies department as well as History.
In a high school context, history is a subset of social studies, although there are also social studies that are not history (civics / government / political science, economics, psychology, geography).
How/where are you being asked to report it?
If they have no definitions of the classifications, the above is standard.