There are 2,100 bacteria in a circular petri dish. the dish has a radius of 40 millimeters. what is the approximate population density?

Population: 2,100 bacteria
petri dish radius : 40 millimeters

Area of a circle = π r²
A = 3.14 * (40mm)²
A = 3.14 * 1,600 mm²
A = 5,024 mm²

Population density is the measurement of the population per unit area or unit volume:

population / area  = 2,100 / 5,024mm² = 0.41799
 
The approximate population density is 0.42 bacteria per square millimeter

In all honesty, there really is no “work” per say to show. mainly it’s just using the process of elimination. the question is asking which domain(s) would be the most appropriate for the function c(n). n is the number of observed vehicles so right away, 1, 2, and 3 can be eliminated.why? 1, 2 start in the negatives and therefore it is impossible to observe negative cars. so, #4 would be the best answer to the given problem.