Answer:

Rule 15-1 states “a player must hole out with the ball played from the teeing ground …”. Additionally, Decision 27-10 provides guidance when there are two balls with identical (or no distinguishable) markings are found in the same area. [ Did Player A play a stroke with his original ball? There is a 50/50 chance that he did – somewhat less than meeting the requirement of “must”.] Also, see Decision 12-2/1.

Player A has played a wrong ball, incurring a two-stroke penalty, and must return to where he last played under a penalty of stroke and distance - total penalty of three strokes.