Context: Easter was the Sunday after the 15th day of this moon, whose 14th day was allowed to precede the equinox. Where the two systems produced different dates there was generally a compromise so that both churches were able to celebrate on the same day. By the 10th century all churches (except some on the eastern border of the Byzantine Empire) had adopted the Alexandrian Easter, which still placed the vernal equinox on 21 March, although Bede had already noted its drift in 725—it had drifted even further by the 16th century.

Question: When was Easter Sunday celebrated after the equinox?
Answer: 15th day

Question: What did churches do to settle the date if there was a difference? 
Answer: compromise

Question: By what century had almost all churches begun celebrating Easter according to the Alexandrian Easter?
Answer: 10th century

Question: On what border of the Byzantine Empire were the last holdouts for celebrating according the  Alexandrian Easter?
Answer: eastern border

Question: What date placement drifted increasingly off the true date on the calendar?
Answer: vernal equinox

Question: What was celebrated on the fifteenth day after the equinox?
Answer: Unanswerable

Question: In what century did all the churches adopt the Alexandrian Easter?
Answer: Unanswerable

Question: Who noticed the equinox drift in the seventh century?
Answer: Unanswerable

Question: What did the Alexandrian Easter place on 25 March?
Answer: Unanswerable