For table cover
l = 4 – (0.25 + 0.25)
| ∵ 25 cm = 0.25 m
= 3.5 m b = 2 – (0.25 + 0.25) = 1.5 m
∴ Area of the cover = l x b
= 3.5 x 1.5 = 5.25 m² Cost of polishing the top of the table at र 40 per square metre = 5.25 x 40 = र 210.

Let the length and the breadth of the room be 4x m and x m respectively.
Area of the four walls of the room = 2(l + b) h
= 2(4x + x) 5 = 50 x m²
Cost of papering the four walls of the room @ 70 paise per square metre
= र 50x x 0.70 = र 35x According to the question,
35x = 157.50

∴ Breadth of the room = 4.5 m
∴ Length of the room = 4 x 4.5 m = 18 m. 

For tank
I = 12 m b = 9 m h = 4 m Total surface area of the tank
= 2 (I x b + b x h + h x l)
= 2(12 x 9 + 9 x 4 + 4 x 12),
= 2(108 + 36 + 48)
= 2(192) = 384 m² Width of the iron sheet = 2 m

∴ Length of the iron sheet = 

Cost of the iron sheet = 192 x 50 = र 9600.

For classroom
l = 1 m b = 6.5 m h = 4 m Area to be colour washed
= 2(l + b) h – [3 x 1.4 + 3 {2 x 1}] = 2(7 + 6.5) 4 – (4.2 + 6)
= 108 – 10.2 = 97.8 m²
Cost of colour washing = 97.8 x 3.50 = र 34.30

Let the height of the hall be h m.
Area of the floor = l x b
= 20 x 16 = 320 m² Area of the flat roof = l x b
= 20 x 16 = 320 m² Sum of the areas of the four walls = 2(l + b) h
= 2(20 + 16) h = 72 h m² According to the question,
72 h = 320 + 320



Hence, the height of the hall is