To solve this, the first thing we are going to do in convert 15 km to meters to see which one is the distance of the long runs. To do that we are going to take advantage of the fact that

, and with this we are going to set up a conversion fraction as follows:

We now now that the ditance he covers in his long run days is

, and in his short run is

.
Lets find out the distance he will cover on
his two long run days:

Likewise, lets find the distance he will cover in his short run days:

Now, we just need to find the difference between the tow distances:

We can conclude that we will run 13,000 meters further in his long runs than in his short runs.