When conducting historical research, it is important to use primary sources for one main reason. This is because anything can be made up from secondary and third hand sources. A primary sources means it comes straight from the person, these are one of the most reliable sources you can include in anything.
The Nile River Valley Civilization started at the northern most peak of the Nile River at the time of the Neolithic Revolution. This early civilization formed down the lush fields of the Nile River. Protected by the water and desert, the civilization was able to grow into Egypt and surrounding colonies. hope this helps.
From the year of 1760 to 1820 or 1840 (one those could be your answer so.
1820years - 1760years =
60years
or if its the other year (1840)
Then try going with 1840years - 1760years = 80 years
So, either 60 years or 80 years would most likely be your answer! (If that's one of your options )