If f(x) is the slope of a trail at a distance of x miles from the start of the trail, what does 9 f(x)dx 3 represent? The change in the elevation between x = 3 miles and x = 9 miles from the start of the trail. The elevation at x = 9 miles from the start of the trail. The elevation at x = 9 miles from the end of the trail. The change in the elevation between x = 3 miles and x = 9 miles from the end of the trail. The elevation at x = 3 miles from the start of the trail.