In this question, the asker wants to know how to calculate the distance. One calculates distances through mathematical equations. In this case, the equation is called the law of cosines and is a more general form of the Pythagorean theorem.
The hard-science tag was removed with an edit reason of
Removed hard-science tag, because this is in essence an elementary math problem with one definite answer, so it is not appropriate to ask for evidence.
Is that correct?