To answer this question, we need to remember the concept of rate. A rate is a result of comparing two different quantities, numbers. It is also a ratio - the result of dividing two numbers. In this case, we have two different quantities (or numbers):
1. Square miles that indicate the measurement of area. In this case, 326 square miles or 326 mi².
2. Population. In this case, we have 6846 residents.
In general, we can express the relationship if we divide the population by the area of the county, as the question suggests. Then, we have:
[tex]rate=\frac{Population}{Area}\Rightarrow rate=\frac{6846\text{residents}}{326mi^2}\Rightarrow rate=21\frac{residents}{mi^2}[/tex]
Therefore, the rate that best represents the relationship between the population of the county and the area of the county is 21 residents per square mile (option C).
