
Shortcut Trick
Total area to paint = Area of 4 walls + Area of ceiling
Total area = 2 × h × (l + b) + (l × b)
Total area = 2 × 3 × (7 + 5) + (7 × 5) = 72 + 35 = 107 m2
Total Cost = 107 × 16 = ₹1,712
∴ The correct answer is ₹1,712.

Alternate Method
Given:
Length (l) = 7 m, Breadth (b) = 5 m, Height (h) = 3 m
Rate of whitewashing = ₹16 per m2
Formula Used:
Area of 4 walls (Lateral Surface Area) = 2h(l + b)
Area of ceiling = l × b

Calculations:
⇒ Area of 4 walls = 2 × 3 × (7 + 5) m2
⇒ Area of 4 walls = 6 × 12 = 72 m2
⇒ Area of ceiling = 7 × 5 = 35 m2
⇒ Total area to be whitewashed = 72 + 35 = 107 m2
⇒ Total Cost = Total Area × Rate per m2
⇒ Total Cost = 107 × 16 = 1712
∴ The correct answer is ₹1,712.

Additional Information
Total Surface Area of a Cuboid
Includes the area of all 6 rectangular faces: 2(lb + bh + hl).
Lateral Surface Area (Area of 4 walls)
Excludes the top (ceiling) and bottom (floor) faces: 2h(l + b).
Length of Longest Diagonal
The longest rod that can be placed inside a cuboidal room is its main diagonal: √(l2 + b2 + h2).