(1) 9*4 - 4c = x
(2) 9*2 +2c = x
∴ 36 - 4c = 18 + 2c
18 - 4c = 2c
9 - 2c = c
9 = 3c
c = 3 mph
I would say c is the correct answer as if there is a low birth rate, when the population ages you are going to have lots of people retiring and not as many people working and paying taxes so pressures on pensions and social security programs will rise. Hope this helps :)
Https://www.tamaqua.k12.pa.us/cms/lib07/PA01000119/Centricity/Domain/119/TheAgeofImperialism.pdf
