the monument, the radius, and the hypotenuse from the center of the circle to the top of the monument form a 30-60-90 right triangle
the building, the radius, and the hypotenuse from the center of the circle to the top of the building form another 30-60-90 right triangle
in a 30-60-90 right triangle, the longer side is equal to the shorter side times √3
in one triangle the radius is r, the shorter side, and the longer side is r*√3
in the other triangle the radius is r, the longer side, and the shorter side is r/√3
the longer side, r, is √3*shorter side which makes the shorter side r/√3 so (r/√3)*√3=r
the height of one building is r*√3 and the height of the other building is r/√3
the ratios of the heights is either r√3/(r/√3)=√3√3=3 or 3/1, or...