Question 757175
The sense best found is that this is arithmetic progression.

YEAR_______0 is year 2009__________POPULATION(Billions)
2009_______0__________6.8
2010_______1__________{{{6.8+0.07}}}
2011_______2__________{{{6.8+0.07+0.07}}}
(???)______n__________{{{6.8+0.07n}}}


What is n when the population is 8.5 billion?  Then the year is {{{2009+n}}}.


{{{6.8+(0.07)n=8.5}}}
Find n.