The length of the rectangle is 45 mm, and the width is 3 times less. Find the perimeter of the rectangle.

For calculations, we will immediately translate the data indicated in the tasks to the given unit of measurement – centimeters, knowing by definition that one centimeter contains 10 millimeters:
45: 10 = 4.5.
Determine how many centimeters the width of the specified rectangle is, knowing by the problem statement that it is three times shorter than the length:
4.5: 3 = 1.5.
Determine how many centimeters the perimeter of this rectangle equals:
2 * (4.5 + 1.5) = 12.
Answer: The perimeter of the rectangle is 12 centimeters.