I'm pretty sure that this is not an official GMAT question (which I will explain shortly) but here it goes:
Imagine a square (the patio) which is "framed" by a larger square (the walkway).
x is the width of the walkway, so each side of the patio is x+5 meters long.
The outer edges of the walkway will be (x+5)+x+x or simple 3x+5
The area of the larger, outer square MINUS the area of the patio will EQUAL the area of the walkway.
So, our equation is (3x+5)^2 - (x+5)^2 = 132
If we simply this we get 8x^2 + 20x = 132
Set equal to zero to get 8x^2 + 20x - 132 = 0
Divide both sides by 4 to get 2x^2 + 5x - 33 = 0
Here's where I conclude that this is not an official GMAC question. Even though GMAC suggests that students need to know how to solve quadratics where the coefficient of the x^2 is not zero (and the quadratic is neither a square or a difference of squares) I have never seen an official question that tests this skill, and I've looked a lot of GMAT questions. That said, perhaps it is a real GMAT question (750+ level at that), so let's solve this quadratic. It's not that hard to factor.
Factor to get (x-3)(2x+11)=0
We get x=3 or x=some negative number.
Since x must be positive, x must equal 3.
This means the sides of the patio are 8 meters long, which means the area of the patio is 64 square meters.