Answer:
Hey!
Your answer is 3.5cm!
Explanation:
We are given one side's length... 8.5cm
As there are 2 sides we add (or multiply by 2) these sides together...
8.5 + 8.5 = 17
We are missing two shorter sides now...
So we have to divide 17 by 2 to get...
17 / 2 = 3.5! *this is your answer!*