Law of reflection of mirrors states that the angle of incidence is equal to the angle of reflection.
In the current scenario, the reflected ray is what Wilma sees while from the top of the tower to the mirror is the incident ray.
Using trigonometry, Wilma's eye, Wilma's foot and the mirror forms a right angled triangle with one leg being 5 ft and the other being 5.5 ft.
Therefore,
Angle of incidence, i = tan^-1 (5.5/5) = 47.726°
Angle of reflection, r = angle of incidence, i = 47.726°
Similarly, tan r = 75/Height of tower => Height of tower = 75/tan 47.726° = 68.1818 ft
Rounding to nearest ft;
Height of the tower = 68 ft