The description is not perfectly clear.... I will assume the 9.45 meters and 2.75 meters are the distances from Madeline and the building from the X -- and not the distances to the edges of the mirror.
Use corresponding parts of similar triangles.
Madeline's eyes height building's height
-------------------------- = --------------------------
Madeline's distance from X building's distance from X
1.55 x
---- = ----
2.75 9.45
x = ((1.55)(9.45))/(2.75)
Use a calculator....