Question 478812
We take a point p= (x,y) the the result of rotation p 90 clockwise about the origin is a new point p'=(x',y')= (-y, x).

ex:

In the case of p=(1,0) the new point is p'= (0, -1)

so, in your case it will be:

for p=(-2,4) the new point is p'= (4, -(-2))=(4,2)