The problem can be solved with a trigonometric analysis. Since the question gives away the fact that the slide is 3 meters above the ground, and is include at an angle of 30 degrees, we can create an image with the slide forming a triangle. Obtaining the displacement (hypotenuse of the created image), we take the sine of the angle:
sin 30 = 3/s
where: s = displacement
s = 3 / sin 30
s = 6
Therefore, Nancy's displacement is 6 m each time she slides down from the top.