An opinion is a statement based on personal judgments, beliefs or ideas and therefore all opinions are subjective and cannot be proven. On the other hand, a fact is an objective statement, this means it does not depend on the perception of people but represents reality and therefore can be proven.
In the case of "There are 54 states in the United States," this is not an opinion because this statement can be proven or disproven as you can look on the library, internet, etc. for the number of the United States and the answer will be the same, which means it does not depend on the perception of people
