The length, breadth and height of a room are 1, b and h respectively. The perimeter of the ceiling expressed as a percentage of the total area of the four walls is

Perimeter of the ceiling (a rectangle of sides 1 and b) is 2(1 + b) — the standard perimeter formula for polygons (rectangle) [1]. The total area of the four walls equals 2 × (length + width) × height = 2(1 + b)h, since the combined area of opposite walls is perimeter × height. Therefore the perimeter expressed as a percentage of the total wall area = [2(1 + b) / 2(1 + b)h] × 100% = (1/h) × 100% = 100/h percent. Hence option 2 (100/h) is correct.

Sources

1. [1] https://www.roguecc.edu/dept/math/PDF/MTH63-3rdEdition.pdf