In a quadrilateral PQRS, $$\angle{S}$$ = 90°. A circle (o, r) touches the sides PQ, QR, RS and SP at A, B, C and D respectively. If QR= 38 cm, RS = 25 cm and QA = 27 cm, find 'r'.

A

16 cm

B

12 cm

C

14 cm

D

10 CM