Set up a chart like this:

Kelly  
2j(twice the number) - 3 (three less than)

Jon
j(unknown)

Since both equal 4, set the equation equal to 4.

2j-3+j=4

Combine like terms to get:

3j-3=4
  +3+3
3j=7
3  3

j=2.33 miles

Now that you know that Jon rode 2.33 miles, you can use 2j-3 to figure out that Kelly rode 1.66 miles.