Linearly means we can just get the average per year and then multiply by the number of years...
from 1960 to 1996 is 36 years
450 000 to 500 is a drop of 449500 cases
-449 500 / 36 = - 12486.11 cases per year
from 1960 to 1987 is 27 years
450 000 - 27 yr * 12486.11 cases/year = 112875 cases