Our estimated equation for the line is `y=-81.24 t+164text[,]599`, but there is no unique answer. We calculated a slope from the first and last points. Then we used that slope and one of the points to determine the equation for the line. This equation leads to an estimate of a per capita consumption of 1,956 cigarettes in 2002. Whether you agree with that estimate or not depends on the correctness of your (and our) calculations. You also have to accept our implicit assumption that the linear pattern would continue for at least two more years. (In fact, the number reported for 2002 was 1,979.)
Important: If you had difficulty with any of the steps in the preceding paragraph, stop right now and straighten out whatever went wrong. What are the coordinates of the two points determining your line? Do the `y`-coordinates make sense in terms of the graph? How do you calculate slope from the coordinates of the two points? Once you know the slope `m`, how do you find `b`? You don't have the luxury of substituting `t=0`, because that is not a year that makes sense in the current setting. However, you can substitute either of your known pairs of `t` and `y` to get an equation in which `b` is the only unknown. Once you have sensible values for `m` and `b`, the calculation is straightforward with a computer algebra system or your calculator.