Let's start out with what we know:
We have two sections: long (L) and short (S).
Together, those sections must equal 28ft so the equation would look like this:
L + S = 28ft
Now, we also know that the longer section is three times as long as the shorter one. That can be written in an equation as well:
L = 3S
Since we know L = 3S, we can substitute that into the first equation like this:
L + S = 28ft
(3S) + S = 28ft
4S = 28ft
4S/4 = 28ft/4
S = 7ft
So the shorter portion is 7ft long
