The bar graph shows the percentage of Americans who used cigarettes, by ethnicity, in 1985 and $2005 .$ For each of the groups shown, cigarette use has been linearly decreasing.
In this exercise, let $x$ represent the number of years after 1985 and let $y$ represent the percentage of Americans in one of the groups shown who used cigarettes.
a. Use the data points (0,38.9) and (20,27.3) to find the slope-intercept equation of the line that models the percentage of whites who used cigarettes, $y, x$ years after $1985 .$
b. Use the data points (0,40) and (20,24.2) to find the slope-intercept equation of the line that models the percentage of Hispanics who used cigarettes, $y, x$ years after $1985 .$
c. Use the models from parts (a) and (b) to find the year, to the nearest whole year, during which cigarette use was the same for whites and Hispanics. What percentage of each group, to the nearest percent, used cigarettes during that year?