Complex Numbers

Let \(w_{1}\) be the point obtained by the rotation of \(z_{1}=5+4 i\) about the origin through a right angle in the anticlockwise direction, and \(w_{2}\) be the point obtained by the rotation of \(z_{2}=3+5 i\) about the origin through a right angle in the clockwise direction. Then the principal argument of \(w_{1}-w_{2}\) is equal to :