From House to School

Questions: How far is your house from Parish? What is the average speed you experience when traveling home from school?

Parish Episcopal School is about 6.86 miles from my house. I used Google Earth to get the measurement to measure the route I take to get to school, considering that Google Maps does not have the exact route I take. To get to school, on average, it takes about 20 minutes, and the average speed my parents drive is 34.5 mph. I know the average speed is 34.5 mph because my parents keep driving at 35 and 34, which added together and divided by two will give me 34.5. If I were to use my data in the speed formula, it would come out nearly exact. The equation is 34.5 = 6.86/20, which at first will get 0.343, but you have  to move the decimal point twice to get 34.3 mph, yet it was off by a few decimal points. If I were to convert it to meters per second, I would just have to multiply  34.5 mph to 1609.344 meters (there are that many in a mile) and divide it by 3600 seconds. This would get me 15.333472 meters per second.