To find the breadth of the rectangle, we need to use the formula for the perimeter of a rectangle, which is given by:

Perimeter = 2(length + breadth)

Given that the perimeter is 240 dam and the length is 1.5 dam, we can substitute these values into the formula:

240 = 2(1.5 + breadth)

Simplifying the equation:

240 = 3 + 2breadth

Subtracting 3 from both sides:

237 = 2breadth

Dividing both sides by 2:

breadth = 237/2

Therefore, the breadth of the rectangle is 118.5 dam.