For this case we know that the exit to Johnstown is 1 3/4 miles away and the exit to Jerrystown is 4 1/2 miles away and we want to find the distance from Johnstown to Jerrystown. And in order to do this we just need to take the difference between the two fractions, but let's convert the values like this:

Then the distance between thw two cities is given by:

Final answer: 11/4 mi or 2.75 mi