A wild horse runs at a rate of 8 miles for 6 hours. Let f(x) be the distance in miles, the horse travels for a given amount of time, x, in hours. This situation can be modeled by a function. What is the domain of the function?

a. 0 < x < 6

b. 0 < f(x) < 6

c. 0 < x < 48

d. 0 < f(x) < 48