Please help me with this question, I can't figure out which one is the independent variable and dependent variable?

Year--- Number of Tourists (1,000,000)--- Ridership (100,000)

1-----------------8---------------16

2-----------------3---------------11

3-----------------7----------------14

4-----------------5----------------16

5-----------------15--------------26

6-----------------16---------------28

7------------------17--------------25

8-----------------13----------------15

9------------------15----------------28

10-----------------21----------------45

Springfield Massachusetts has long been known as a top vacation spot in the country, due largely to its beautiful weather, the Basketball Hall of Fame, and the home of Dr. Seuss. Peter Pan Bus Lines is a travel company specializing in providing public transportation to the region, and would like to make preparations for the upcoming year. Springfield city officials are expecting 17 million (17,000,000) tourists over the next year. As part of the planning process, Peter Pan has accumulated statistics for the past ten years pertaining to the total number of Springfield tourists, as well as the number of customers (i.e., ridership). 

Using the equation y=mx+b, what is the predicted number of ridership over the next year (i.e., assume that there are expected to be 17,000,000 tourists; 17 million tourists