Consider the quadratic model.

Where represents the number of years after 1960 and represents the percent of people over 19 years of age who have ever smoked and quit.

(a)

Consider one solution of the equation is .

This means after 40 years, 58.5 percent of people over 19 years of age who have ever smoked and quit.

That is after the year 2000, 58.5 percent of people over 19 years of age who have ever smoked and quit.