If you look at the graph, you notice there is no data to determine the slope, but there (0,b) represents the y-intercept. So my guess is, they give you a clue what the slope is already, but if you notice the y-intercept lowers the linear line a few notches because (0,18) is lower than the (0,30). That is what I would choose as the answer
so you add 5.5 from 19 to get the answer