Lionel walks 8 miles before Walt starts walking (2hrs @ 4mph)
Together they have to "manage" 40 mile distance. While we could use combined rate to figure the time both spent, it is not necessary (though it would be 4 hours). Since the rates of the speeds are in the ratio of 2:3, Lionel walks 40% of the distance (and Walt 60%), or 40miles*40%=16 miles.
16+8 = 24 --> total miles Lioned walked.
There are times when I do not mind kudos...I do enjoy giving some for help