Answer:
To find vertices that has been rotated 270 degrees, you would want to apply this rule to the point ; (x,y) (x, -y). This rule is the same as negative 90 rotation.
So, we have the coordinates (-4,0) , (5,2) , (-2,-3).
We can apply the rule to all three coordinates turning the y values negative.
We end up with
G = (-4, 0)
H = (5, -2)
I = (-2, 3)