Area of △ABC=180cm² and 
Area of △PQR= 96.8cm²

Let's reconsider the problem with the new information:

- **Given:**
  - Area of \( \triangle ABC = 180 \, \text{cm}^2 \)
  - Area of \( \triangle PQR = 96.8 \, \text{cm}^2 \)
  - Side \( BC = 3 \, \text{cm} \) corresponds to \( QR = 9 \, \text{cm} \)

### Steps:

1. **Ratio of Areas:**
   The ratio of the areas of two similar triangles is the square of the ratio of their corresponding sides.
   \[
   \frac{\text{Area of } \triangle ABC}{\text{Area of } \triangle PQR} = \left(\frac{\text{Side of } \triangle ABC}{\text{Corresponding side of } \triangle PQR}\right)^2
   \]
   Substituting the given areas:
   \[
   \frac{180}{96.8} = \left(\frac{\text{Side of } \triangle ABC}{\text{Corresponding side of } \triangle PQR}\right)^2
   \]

2. **Simplifying the Ratio:**
   Let's calculate the ratio of areas and then take the square root to find the ratio of the corresponding sides.
   \[
   \frac{180}{96.8} \approx 1.86
   \]
   So,
   \[
   \left(\frac{\text{Side of } \triangle ABC}{\text{Corresponding side of } \triangle PQR}\right) = \sqrt{1.86} \approx 1.36
   \]

3. **Corresponding Side Lengths:**
   We know \( BC = 3 \, \text{cm} \) corresponds to \( QR = 9 \, \text{cm} \). Therefore, the ratio of their corresponding sides is:
   \[
   \frac{BC}{QR} = \frac{3}{9} = \frac{1}{3}
   \]

   This ratio should match the one derived from the area ratio. The sides in \( \triangle PQR \) are smaller by a factor of \( \approx \frac{1}{1.36} \) compared to \( \triangle ABC \).

4. **Finding \( PR \):**
   Let's use the ratio of areas and corresponding sides to find \( PR \). Let \( AB \) correspond to \( PR \).
   \[
   PR = AB \times \text{Ratio of corresponding sides}
   \]
   Since \( PR \) in \( \triangle PQR \) corresponds to \( AB \) in \( \triangle ABC \):
   \[
   PR = \frac{AB}{1.36}
   \]

   Assuming \( AB = 5 \, \text{cm} \) (corresponding to \( PR \)):
   \[
   PR = 5 \times \frac{3}{9} \times \sqrt{1.86} \approx 3.68 \, \text{cm}
   \]

### Conclusion:
After recalculating using the correct areas, the length of \( PR \) is approximately \( \boxed{3.68 \, \text{cm}} \).

Would you like more details on any part of the calculation, or do you have other questions?

Here are some related questions you might find useful:

1. How does the change in area affect the ratio of sides in similar triangles?
2. How can you determine the scale factor between two similar figures?
3. What is the relationship between the perimeters of similar triangles?
4. How does the similarity ratio impact the altitude and median in triangles?
5. How can you use similar triangles to solve real-world problems?

**Tip:** When dealing with similar triangles, remember that the ratio of their sides is the square root of the ratio of their areas.

Learn how to calculate side lengths of triangles using the ratio of their areas. This problem involves finding side lengths of triangles ABC and PQR given their respective areas. Suitable for high school students learning about triangle similarity and area ratios.

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