Final answer:
To estimate the number of people in the city who have visited the garden, you can use the proportion of butterfly visits per flower per day in various fields throughout the growing range of the plant.
Step-by-step explanation:
To estimate the number of people in the city who have visited the garden, one possible expression to use is the proportion of butterfly visits per flower per day in various fields throughout the growing range of the plant. This expression assumes that the number of butterfly visits can be used as an approximation for the number of people visiting the garden.