In question 7, the exercise only wants an explanation, in text form, of the meaning of the substitutions. That is, that the value of x=5 indicates the time that has passed, 5 hours, and that f(5)=32 indicates the number of riders.
In question 8, you need to pick some values for x, make a table with those values and the respective values of the function when you substitute those values of x, and put the points on the graph.
