(3) l + b + h = 18 metre l : b : h = 3 : 2 : 1 Sum of the terms of ratio = 3 + 2 + 1 = 6 ∴Length =
3
6
×18=9 metre Breadth =
2
6
×18=6 metre Height = 3 metre ∴ Area of the four walls ofroom = 2 × h (l + b) = 2 × 3 (9 + 6) = 90 sq. metre. ∴Total cost of painting = Rs. (15 × 90) = Rs. 1350