Mr. Barker saved his money for forty-seven years and had three million, seven hundred thousand, twenty-eight dollars in the bank. He used his money to go on an adventure and spent four hundred ninety-seven thousand, four hundred dollars. How much did he have left after his adventure?

5.5 miles over 2 hours--> 5.5/2= 2.75 miles per hour was his average walking speed. 5.5 miles over 2.5 hours --> 5.5/2.5= 2.2 miles per hour on the return trip meaning that his average speed was (2.75-2.2= 0.55) 0.55 miles per hour lower on the return trip