Answer:
7686 people per square mile
Explanation:
The total area of the coastal city = 92.1 square miles
Area covered by water = 11.3 square miles
Population of the city in 2010 = 621,000
Now we use the formula
Population density =

=
= 7686 people
The population density 7686 people per square mile of land area of the city at that time.