Calculation:

From the figure, it is noticed that two similar triangles formed due to height of a person and his distance from mirror with the height of the wall and its distance from mirror.

In order to find the height of a wall, it is enough to implement the similarity definition on the triangles.

Thats, the similar triangles obey the proportionality of the corresponding length of the sides of the triangles each other.

Hence, from the given triangles the proportionality of the length of the sides is,

\(\displaystyle\frac{{{T}{B}}}{{{H}{F}}}=\frac{{{M}{B}}}{{{F}{M}}}{\left\langle'\le{t}{h}{e}\ {h}{e}{i}{g}{h}{t}\ {o}{f}\ {w}{a}{l}{l}={x}\right)}\)

\(\displaystyle\frac{{x}}{{5.5}}=\frac{{20}}{{2.5}}\)

\(\displaystyle{x}=\frac{{{\left({20}\right)}{\left({5.5}\right)}}}{{{2.5}}}\)

x=44ft

Thus, the height of the wall is 44 ft.