Problem:
The length of a rectangle is 6 metres less than twice its breadth. The perimeter of the rectangle is 240 metres. Find its breadth.

Solution:
Let's solve the problem step by step:

Step 1: Understand the problem:
We are given that the length of a rectangle is 6 metres less than twice its breadth. We need to find the breadth of the rectangle.

Step 2: Assign variables:
Let's assume that the breadth of the rectangle is 'b' metres. We can then express the length of the rectangle in terms of 'b'.

Step 3: Express the length in terms of the breadth:
According to the given information, the length of the rectangle is 6 metres less than twice its breadth. Therefore, the length can be expressed as: 2b - 6.

Step 4: Write the perimeter equation:
The perimeter of a rectangle is given by the formula: Perimeter = 2(length + breadth).
In this case, the perimeter is given as 240 metres. So, we can write the equation as:
240 = 2(2b - 6 + b)

Step 5: Solve the equation:
Let's solve the equation to find the value of 'b'.
240 = 2(3b - 6)
240 = 6b - 12
6b = 240 + 12
6b = 252
b = 252/6
b = 42

Step 6: Check the solution:
To check if our solution is correct, we can substitute the value of 'b' back into the equation for the length:
Length = 2b - 6
Length = 2(42) - 6
Length = 84 - 6
Length = 78

Step 7: Final answer:
The breadth of the rectangle is 42 metres.

Length - 6m
perimeter - 240 m
breadth - 6/240
breadth - 40 m