Function f (x) represents the population of bacteria x hours after 9 a. m. What does f (2) - f (1) represent?

x = number of hours after 9 am (eg: x = 1 means 1 hr after 9 am, so 10 am)

f (x) = population count x hours after 9 am

f (1) = population count at 10 am (1 hour later)

f (2) = population count at 11 am (2 hrs after 9 am)

f (2) - f (1) represents the difference in population counts from 10 am to 11 am, or put another way, how much the population increased during that time interval.