Ascientist counted 3921 total eggs in 49 sea turtle nests. there were about the same number of eggs in each nest. which is a reasonable estimate of the number of eggs she counted in each nest?

3921 / 49 = 80 
You are trying to find out how many 49's go into 3921, to do this, you have to take 3921 and divide it by 49, this will tell you how many eggs are in each nest.
Alternatively, the question could have said there are 3921 total eggs, and approximately 80 eggs in each nest, how many nests were there?
Here we'd go ahead and divide 3921 by 80 to get 49.