Answer:
About 6,785 people will be infected about nine months.
Step-by-step explanation:
We can write an exponential function to represent the situation. The standard exponential function is given by:

Where <em>a</em> is the initial value, <em>r</em> is the rate, and <em>x</em>, in this case, is the time that has passed in months.
3,124 people have already been infected. Thus, our initial value <em>a</em> = 3124.
And an additional 9% will be infected per month. Therefore, our rate <em>r</em> will be 1 + 9% or 1.09.
Hence, our function is:

Then after nine months, the total amount of infected people will be f(9):

Use a calculator:

About 6,785 people will be infected about nine months.