County $Y$ consists of two districts. One district has an area of 35 square miles and a population density of 390 people per square mile, and the other district has an area of 50 square mile population density of 300 people per sq. mile. What is the population density in people per sq. mile, for all county $Y$ ?

Question

$\begin{array}{1 1} (a)\; \text{320 people per sq. mile} \\ (b)\; \text{322 people per sq. mile} \\ (c)\; \text{325 people per sq. mile} \\ (d)\; \text{326 people per sq. mile} \end{array}$