One model of earth's population growth is p(t)=64/(1+11e^-.08t)

The question may be incomplete.  

I guess the answer is as follows:

 we are given the function adn we can see that when t is increased, P(t) is decreasing because of the negative sign. This means the value of the population which is the original of 64 billion will have to decrease.The answer that makes sense here is D. D. In 1990, there were 5.33 billion people.

points are handed out whenever you post answers.

brainliest answers are handed out by the person asking the question, so whether your answer is picked depends entirely on whether the asker bothers to pick

if you're asking about your rank, it depends on having a certain number of points and a certain number of brainliest answers. for example, at the time of this writing, i have 44338 points out of 15000 needed for the next (nearly triple the requirement! ) but i only have 24 out of 50 required brainliest answers. this number decays, meaning after a certain amount of time (i think about a month), the total number of brainliest answers you've earned doesn't count toward this total. (i've been stuck at the same rank for a long

the lesson to learn here is that you shouldn't worry about points or rank. chances are, no matter how good an answer you may provide, your efforts will go mostly unnoticed unless you focus on the newest/most active questions that get posted.

yes because there is exactly one y value for every x value

for function there can't be more than one value for every x value