=4-19 Bus and subway ridership in Washington, D.C., during the summer months is believed to be heavily tied to the number of tourists visiting the city. During the past 12 years, the following data have been obtained:

Year Number of Tourists

(1,000,000s)

Ridership

(100,000s)

1 7 15 2 2 10 3 6 13 4 4 15 5 14 25 6 15 27 7 16 24 8 12 20 9 14 27 10 20 44 11 15 34 12 7 17

(a) Plot these data and determine whether a linear model is reasonable.

(b) Develop a regression model.

(c) What is expected ridership if 10 million tourists visit the city?

(d) If there are no tourists at all, explain the predicted ridership.