Given,

Dimensions of room = 9m × 8m × 6.5m

Area of 4 walls = 2 (length + breadth) × height = 2 (9 + 8) × 6.5 = 13 × 17 = 221 m²

Dimensions of one door = 2m × 1.5m

Area of door = length × breadth = 2 × 1.5 = 3.0 m²

Dimensions of windows = 1.5m × 1m

Area of 2 windows = 2 (l × b) = 2 (1.5 × 1) = 3.0 m²

Hence,

Area required for white-washing = Area of 4 walls – (area of door + area of 2 windows)

= 221 – (3 + 3) = 221 – 6 = 215 m²

∵ cost of white-washing 1 m² area = Rs. 6.40

∴ cost of white-washing 215 m² = 6.40 × 215 = Rs. 1376.