Explanation:

- The ratio of the length to the breadth of the rectangle is given as 5:4.

- Let's assume the length is 5x meters and the breadth is 4x meters.

- Area of the rectangle is length × breadth, which is 5x × 4x = 20x² square meters.

- The cost to paint the floor is Rs. 1500 at the rate of Rs. 3 per square meter.

- So, the area of the floor is 1500 / 3 = 500 square meters.

- Therefore, 20x² = 500, solving gives x² = 25, so x = 5.

- This means the length is 5x = 25 meters and the breadth is 4x = 20 meters.

- The difference between the length and breadth is 25 - 20 = 5 meters.

- The correct option is 3, which is 5 m.

.