Answer:
The answer is 
Step-by-step explanation:
In order to determine the unit rate, we have to know about rates.
In any "rate", the number is representing the fraction of two measures. For example in physics, the velocity is the rate of distance per time, where we divide the distance measure by the time measure.
In this case, we have two measures:
- people.
- square mile.
So, the rate that relates both measures is:

Finally the unit rate is:
