3. (10 points) As shown in the figure, on two identical large rectangular pieces of paper, a small square of the same size is cut from a corner and an edge respectively. If the perimeter of the shaded part in figure (2) is 17 cm more than that of the shaded part in figure (1), then the perimeter of the cut-out small square is $\qquad$ cm.
【Analysis】Observing the figure, we find that the perimeter of the shaded part in Figure (1) is the perimeter of the large rectangle. The perimeter of the shaded part in Figure (2) is the perimeter of the large rectangle plus 2 sides of the small square, meaning the perimeter of the shaded part in Figure (2) is 2 sides of the small square longer than that in Figure (1). First, divide 17 cm by 2 to find the side length of the small square, then use the formula for the perimeter of a square, which is side length $\times 4$ to solve.

【Solution】Solution: $17 \div 2 \times 4=34$ (cm)
Answer: The perimeter of the cut-out small square is 34 cm.
Therefore, the answer is: 34.