Answer:
76,800
Step-by-step explanation:
First, you have to get the area of the town. It's a rectangle, so the formula is LxW (20 x 12). The area is 240 km^2. The question says it has a population density of 320 people per square km, so you just multiply 240 and 320 to get your answer of 76,800.
(Sorry if this isn't explained very well, but it is the right answer)