[
  "Use the perimeter formula: Perimeter = 2 x (Length + Breadth).",
  "Length + Breadth = 30 / 2 = 15 cm. Breadth = 15 - 9 = 6 cm. Ratio breadth : length = 6 : 9.",
  "Simplify 6 : 9 by dividing by 3: 6 / 3 = 2, 9 / 3 = 3. Answer: 2 : 3."
]