4. A commercial airplane travels according to the formula d(t) = 160, where d is the distance traveled in miles and t is the time in hours. What is the meaning of d (320)? A commercial airplane travels at an average speed of 320 miles per hour. It takes the airplane 320 hours to travel two miles. A commercial airplane travels at an average speed of 160 miles per hour. It takes the airplane two hours to travel 320 miles