Insurance companies often try to calculate average life expectancy,
that is, how long different populations can reasonably be expected
to live. The companies do this for men and women and for people
across all ethnicities.
The equation L=0.39y+ 39 is a way of calculating a reasonable
life expectancy for African American females.
This equation is based on y, the number of years after 1900 that
the women were born.
(a) What is the birth year for females who have a life
expectancy of 77 years?