Final answer:
The estimated number of people in the top 1% in 2040 would be 4,000,000.
Step-by-step explanation:
We can estimate the number of people falling into the top 1% in 2040 by using the projected population of 400,000,000. To find the number, we multiply the population by 0.01 (which represents 1% as a decimal). So, the estimated number of people in the top 1% in 2040 would be 400,000,000 x 0.01 = 4,000,000.
Therefore, the correct answer is A. 4,000,000 people would fall into the top 1% in 2040.