Rectangular field ratio 5:4 and breadth 20 m less than length:\nFind the perimeter of the field (metres).

Introduction / Context:
Translate ratio and difference into algebra, solve dimensions, and compute the perimeter.

Given Data / Assumptions:

• L : B = 5 : 4; B = L − 20.

Concept / Approach:
Let L = 5x, B = 4x; then 4x = 5x − 20 ⇒ x = 20 ⇒ L = 100, B = 80.

Step-by-Step Solution:

Verification / Alternative check:
Breadth 80 is indeed 20 less than length 100.

Why Other Options Are Wrong:
260, 280, 320 do not equal 2(180).

Common Pitfalls:
Assigning the difference to the wrong side.

Final Answer:
360m.