Looking at the given image, the height(h) divides the side length of 8 into two equal parts as we see that the height is perpendicular to the side length of 8 m.
Thus, looking at the half triangle of the face where the h is indicated, we can use pythagoras theorem to find h where the hypotenuse is 5 as shown in the diagram since each vertical cross section is an Isosceles triangle. Thus,