we have that
The scale is equal to [tex]\frac{1}{50}[/tex]
That means
[tex]1\ cm\ in \ the \ plan=50\ cm\ in \ the \ actual[/tex]
so
by proportion
Find the actual measurement of the wall marked [tex]18[/tex]cm on the plan
[tex]\frac{1}{50}\frac{plan}{actual}=\frac{18}{x}\frac{plan}{actual}\\ \\x=18*50\\ \\x=900\ cm[/tex]
Convert to meters
[tex]900\ cm=900/100=9\ m[/tex]
therefore
the answer is
[tex]9\ m[/tex]
