Let $$\triangle ABC \sim \triangle RPQ$$ and $$\frac{ar(\triangle ABC)}{ar(\triangle PQR)} = \frac{1}{9}.$$ If $$AB = 3$$ cm. $$BC = 4$$ cm and $$AC = 5$$ cm, then $$PQ$$ is equal to.

A

9 cm

B

15 cm

C

12 cm

D

18 cm