An analyst engaged in the tourism industry obtained detailed information on 76 travel packages offered by a Viennese travel agency. The file Travel contains the following variables:

- Price (price of the package for one person, in \(€\) )

- Distance (distance between departure and destination settlement, in kilometres)

- Mark (mean of former travelers' evaluation of the hotel, based on a scale of 0 to 10)

a. Develop a regression model to predict travel price based on distance.

b. Develop a regression model to predict travel price based on mark.

c. Develop a regression model to predict travel price based on distance and mark.

d. Compute and interpret the adjusted \(r^{2}\) for each of the three models.

e. Which of the three models do you think is the best predictor of price?