#### Answer

a. 2.65 (million)
b. $p=203.3+2.65*x$
c. $335.8$ million

#### Work Step by Step

a. To estimate the yearly average increase, we need to:
1. subtract the value at 1970 from the value at 2010.
$309.3-203.3=106$
2. Divide it by the number of years between them.
$106\div(2010-1970)=106\div 40=2.65$
The estimated average yearly increase is $2.65$ (million).
b. To write the mathematical model ($p$), we need to take the population in 1970 (203.3) and add to it the estimated yearly average ($2.65$) for every year that passed (x).
$p=203.3+2.65*x$
c. Using the model in (b), we can estimate that the population in 2020 will be:
$p=203.3+2.65*(2020-1970)=203.3+132.5=335.8$ (million)