If 1.5 inches on the map represent a distance of 8.1 miles in reality, we can use the proportion:
1.5 inches / 1 inch = 8.1 miles / x miles
where x is the actual distance represented by 1 inch on the map, and is the scale of the map we are looking for.
We can solve for x by cross-multiplying:
1.5x = 8.1
x = 8.1 / 1.5
x = 5.4
Therefore, the scale of the map is 1 inch represents 5.4 miles.