Solution.
There might be different ways to do it but here's how I did it.
First, add up all of the x values: (-3.5) + 0 + 5.5 = 2
then, add up all of the y values: 4.5 - 6.5 - 2.5 = -4.5
Then, use the pythagorean theorem on the absolute value of x and y (disregard the negative signs)...