use the formula of pythagoras theorm:
[tex]a^2+b^2=c^2[/tex]
b = base
c = hypotenuse, the longest side of triangle
a = height/altitude.
we have to find the height. The hypotenuse is given as in 18m and the base is given as in 12m.
[tex]x^2+12^2=18^2[/tex]
[tex]x^2=18^2-12^2[/tex]
[tex]x^2=180[/tex]
[tex]x=\sqrt{180}[/tex]
[tex]x= 13.41[/tex]
