The average speed of mph would be in 10.058. You would first convert the 6 hours to minutes which would be 60*6 and that equals to 360. Now you add the 15 minutes to add all the minutes together. Now it is 360+15 which is 375. You now get the 3,772 miles and divide it by the number of miles, 3,772/375 and it should be 10.058.