This isn't a hard problem once you understand matrix rotations.
[A] -is the original matrix
[r] - is the rotation matrix and
[B] -is the rotated or final matrix
in 2 dimensions
[r]= [cos(θ), sin(θ)
Your point (4,-9) would just be the matrix [A]= [4, -9]
Since counterclockwise is the positive direction you just use θ=150 in the [r] matrix and the do the cross product of [A]x[r]. The result will be the rotated location of your point (or vector).