Hey there, Guest!
So, let's say that the second piece is length x.
The first piece is 3 times that, so it is 3x.
The 3rd piece is 20 feet shorter than it, so it is x-20.
Adding them, we get 5x-20, and that equals 100.
Solving for x, we get 24.
So the lengths are 72, 24 and 4.
Hope this helped! :)
( ゚д゚)つ Bye