Test of Independence · Exercise 8

Transit Railroads is interested in the relationship between travel distance and the ticket class purchased. A random sample of 200 passengers is taken. shows the results. The railroad wants to know if a passenger’s choice in ticket class is independent of the distance they must travel.
$$\begin{array}{ccccc}\text{Traveling Distance}& \text{Third class}& \text{Second class}& \text{First class}& \text{Total}\\ \text{1–100 miles}& \text{21}& \text{14}& \text{6}& \text{41}\\ \text{101–200 miles}& \text{18}& \text{16}& \text{8}& \text{42}\\ \text{201–300 miles}& \text{16}& \text{17}& \text{15}& \text{48}\\ \text{301–400 miles}& \text{12}& \text{14}& \text{21}& \text{47}\\ \text{401–500 miles}& \text{6}& \text{6}& \text{10}& \text{22}\\ \text{Total}& \text{73}& \text{67}& \text{60}& \text{200}\end{array}$$

What is the test statistic?

Its source prints no answer for this problem, so there's nothing to check against.

OpenStax, Introductory Statistics 2e · §11.3 Test of Independence · Exercise 8