Answer: The first answer will be x + 2x = 21
Explain: Piper skated 2 times long, so it gives us the first clue to 2x.
And also, they said the total time spent walking and skating was 21 minutes. And we would also know that the x will be from Piper skated 2 times long so, we know that the x will go first.
Hope this helped. :)
I'm really sorry I could only know the first answer :(