The distance, in miles, a lifeguard can see to the horizon varies directly as the square root of the height, in feet, of the lifeguard's eyes above ground level. Suppose a lifeguard whose eye level is 9 feet above ground can see 3.5 miles to the horizon. How far (in miles) could this same lifeguard see when standing on a lifeguard station that is 13 feet above ground? Round to the nearest tenth of a mile.