Making Linear Predictions?

The number of city and county ordinances that restrict outdoor smoking has increased approximately linearly from 30 ordinances in 1999 to 1124 ordinances in 2007 (Source: American Nonsmoker's Rights Foundation). Let y= the number of ordinances at x years since 1990 a.) Find an equation of a linear model to describe the data b.) Use your equation to predict the year in which there will be 1500 such ordinances. I am stuck this is what I have: 1999 -> 30 ordinances 2007->1124 ordinances points x= years since 1990, y=amount of ordinances for that year (9,30) & (17, 24) M=y2 - y1/ x2-x1 slope: m= 24-30 / 17 - 9 = -6 / 8