2 If a, b,c are in continued proportion a/a+b =a-b/a-c​

If the floor is in rectangular shape

Then your answer is,

Perimeter of rectangle =2(l+b)

18=2(l+b)

Then,

Area \: of \: four \: walls =2(l+b) \times hAreaoffourwalls=2(l+b)×h

Area \: of \: four \: walls=18 \times 3Areaoffourwalls=18×3

Area \: of \: four \: walls =54m²Areaoffourwalls=54m²