We are given coordinate of K point (7,4).
We need to find the new coordinate of K' point.
Given rule is K' = Ro 270°^(k).
That represents rotation of k 270 degree about the origin.
The rule for rotation of 270 degree about the origin is as following:
(x, y) --------> (y, -x).
Now, applying same rule on point (7,4).
(7,4) -----------> (4,-7).