You're on a road trip with your friends. From the start, you drive with an average speed of 50 miles/hour for 6 hours before stopping to have lunch at a diner place for 1 hour.
Then you continue your journey with an average speed of 70 miles/hour for the next 5 hours before reaching downtown and stopping for a supper for 1 hour.
Afterwards, the traffic jam is so bad that you can only use an average speed of 20 miles/hour for 2 hours to arrive at the final destination.
What is the average speed of the whole road trip in miles/hour?