Mark raises guppies in an aquarium. he finds out that guppies reproduce very rapidly, and the number quadruples every month. he starts out with only 2 guppies, and the function y equals 2 times 4 to the x models the number of guppies he will have after x months. which graph represents this function?

For this case what we should know is that the function that best adapts to this problem is given by:
 y = 2 * (4) ^ x
 The graph of the function is shown for two different intervals:
 A small interval of -1.5 to 0.5
 A larger interval of -6.5 to 6.5.
 In both intervals the exponential growth of the function is demonstrated.
 
 See attached image.