There are 3,600 seconds in an hour. Charlie speed is 3-yard per seconds, so multiply it by 3,600 and you'll get 10,800. That means each hour he ran 10,800 yard per hour. There is 1,760 yard per mile.
10,800 divided by 1,760 will equal to 6.13 miles per hour.
6.13 miles per hour is your answer. I hope this helped. :)
