What is the opportunity cost of the first 25 tacos? of the last 25 tacos (from 75 to 100)?

answer; (a) calling people who have not shown interest in the product and asking them to buy it;

answer: a. the kind of population living in your neighbourhood.

the census explorer data tool by the us census bureau allows the user to zoom in on any neighbourhood within the united states and find the kind of people residing in that by race and age.  

the tool needs to needs to be used twice – once in order to find what type of people reside in a neighbourhood, and then to see the age groups of the people in the same neighbourhood.