2. how many years passed between the uniting of upper and lower egypt (before the old kingdom) in about 3100 b. c. to the persians’ takeover of egypt (after the new kingdom) in 525 b. c.?

2,575 years passed between 3100 BC and 525 BC. Calculation of years in the BC era is found by taking the earlier date, or larger number, and subtracting the later or more recent date, the smaller number. 3100 - 525 = 2,575 years.