The first step to solve this problem is to find the area of the region. You do it by using the formula for the area of a circle:
[tex]\begin{gathered} A=\pi\cdot r^2 \\ A=7.5^2\cdot\pi \\ A=176.7 \end{gathered}[/tex]The area of the region is 176.7 square miles.
Now, divide the population by the area of the region:
[tex]D=\frac{1158000}{176.7}=6553.5[/tex]The population density of the region is 6,553.5 people/square mile
