The width of the rectangle is 6 dm, which is 9 dm less than the length. What is the perimeter of the rectangle?

1. If, according to the condition of the problem, the width of the rectangle is 6 dm and is 9 dm less than the length, then its length is 6 + 9 = 15 dm.

2. A rectangle is a figure with 4 sides, and opposite sides are equal to each other.

3. The perimeter of a rectangle is the sum of the lengths of all its sides. That is, the perimeter of the desired rectangle is 6 + 6 + 15 + 15 = 42 dm.