1 inch = 1·500 = 500 miles
2 inches = 2·500 = 1000 miles
3 inches = 3·500 = 1500 miles
4 inches = 4·500 = 2000 miles
5 inches = 5·500 = 2500 miles
...
8 inches = ?·500 = ? miles
The formula is y = 500x, where y is the total number of miles and x is the number of inches you measure.