△ABC ~ △QRP, so the correspondence is: A↔Q, B↔R, C↔P.
Therefore: $\dfrac{AB}{QR} = \dfrac{BC}{RP}$
$\dfrac{9}{QR} = \dfrac{5}{2}$
$QR = \dfrac{9 \times 2}{5} = \dfrac{18}{5} = \mathbf{3.6 \text{ cm}}$
Answer: (D) 3.6 cm
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The key is reading the correspondence carefully: △ABC ~ △QRP means A↔Q, B↔R, C↔P. So AB corresponds to QR (not QP). Students often make errors by matching sides without checking the order of vertices. Use $\frac{AB}{QR} = \frac{BC}{RP}$ and substitute known values to get QR.