In 2009 the life expectancy is about 80 life expectancy gains 5.7 years every decade. From 2009 in how many years would humanity achieve a life expectancy of 120 years

about 70 years

Step-by-step explanation:

Life expectancy (e) improves by 5.7 years every 10 years, so 5.7/10 = 0.57 years per year. For t years after 2009, it can be modeled by ...

e = 0.57t + 80

We want to find when that is 120:

120 = 0.57t + 80

40 = 0.57t

40/0.57 = t ≈ 70.2

About 70 years from 2009, humanity may achieve a life expectancy of 120 years.