Laurie G. answered 10/14/18
Credentialed Teacher Knowledgeable in K-8 Core & Special Needs
The formula would be:
4 + 4 + 5 + 7 + X = 32
You are solving for X, the 5th side.
(4 +4 + 5 + 7) + X = 32
20 + X = 32
<20> <20>
X = 12 (the 5th side)
The reasoning is that all the sides together equal the total perimeter.
I hope this was of help.
Laurie G.