If a population has an annual growth rate of r​ percent, then 70/r is a good estimate of the​ population's doubling time. Use this method to estimate the​ population's doubling time for a country with a growth rate of 1.556​% in 2009.   The estimate predicts that the​ country's population will double in ____ years.

A "Student Drug Use and Health Survey" of Ontario high school students found that the percentage of students that reported serious psychosocial distress in the past month increased from 10.7% in 2013 to 17.1% in 2017. Assuming a standard exponential growth trend, what is the annual growth rate in the percentage of students reporting serious psychosocial distress in the past month?