Given,
Length of hall = 18 m
Width of hall = 12 m
Let height of hall = h metre
Then,
Sum of area of floor & flat roof = l x b+ l x b = 12 x 8 = 432 m2
Sum of area of 4 walls = 2(l x h + b x h) = 2(18h + 12h) = 60 m2
Now,
= 60h = 432 ... ... . .. . .. given
= h = \(\frac{432}{60}\) =7.2 m
Height of hall = 7.2 metre