The population (in millions) of a certain country can be approximated by the function:
P(x) = 50 -1.02",

where x is the number of years after 2000. Which of the following
calculations will tell in what year the population can be expected to reach 100
million?

The first one, i believe, would be correct. all the others have one thing in common, and that's that they have repeating numbers. in the second one, x and y have repeating 6's and 3's, and in the third, x and y have repeating 6's as well. in the last one, there are repeating 3's. the first one has no repeating numbers.