If 3 inches on the map represents 1.25 miles, we can use that proportion to find how many inches represents 10 miles.
3 inches / 1.25 miles = x inches / 10 miles
We can cross multiply and divide to find x:
x = (3 inches * 10 miles) / 1.25 miles
x = 24 inches
So on the map, 24 inches represent 10 actual miles.