For the information given in the statement, the independent variable of the function is h and the dependent variable of the function is n, where n is the number of cars seen by Thomas.
So you have the following table:
Checking the options:
Option a. and b. To know if the function is linear or exponential, you can graph the ordered pairs and see what relationship they have:
As you can see the relationship between the number of hours and the number of cars seen by Thomas is a linear relationship and not exponential. Therefore, the true option is a.
Option c. The common difference is the constant amount of change between numbers in an arithmetic sequence: