Final answer:
The percentage is expected to hit 12% around the year 2030.
Step-by-step explanation:
To determine when the percentage of female adults who smoke in the US will hit 12%, we can assume a linear trend between 2005 and 2013.
First, we need to find the rate of decrease in the percentage:
Rate of decrease = (17.8% - 20.9%) / (2013 - 2005) = -0.31% per year
Next, we can use this rate to determine the number of years it takes for the percentage to reach 12%:
(12% - 17.8%) / -0.31% = 17.42 years
Therefore, the percentage is expected to hit 12% approximately 17.42 years after 2013, which would be around the year 2030.