Giving out 60 points
on a map, the distance between two historical markers is 4.5 inches, and 2.5 inches represents 10 miles.
what is the actual distance between the historical markers?

If the markers are 4.5 inches away on the map, and 2.5 inches represents 10 miles, then we need to make ratios we can work with.

Inches / Miles: 

4.5 / x
2.5 / 10

Now, we can cross multiply to end up with:

2.5 * x = 4.5 * 10

Simplify:

2.5x = 45

Divide 2.5 on each side:

2.5x / 2.5 = 45 / 2.5

Simplify:

x = 45 / 2.5
x = 18

Awesome! Now we have a real ratio on the real distance of the markers.

2.5 : 10  &  4.5 : 18.

18 miles is the actual distance between the two markers.

Hope I could help! If my math is wrong, or it isn't the answer you are looking for, please let me know!
Have a good one!