#### Answer

a. $0.4\%$
b. $34\%$

#### Work Step by Step

a. To estimate the yearly average increase, we need to:
1. subtract the percentage at 1950 from the percentage in 2011.
$30.4-6.0=24.4$
2. Divide it by the number of years between them.
$24.4\div(2011-1950)=24.4\div61=0.4$
The estimated average yearly increase is $0.4\%$.
b. To estimate the percentage for 2020, we need to take the percentage for the last recorded year, 2011, and add it to the estimated yearly average increase, multiplied by the number of years until 2020:
$30.4+0.4*(2020-2011)=30.4+3.6=34$
The estimated percentage of people 25 years of age and older who will be college graduates in 2020 is $34\%$.