From an external point A, two tangents AB and AC have been drawnto a circle touching the circle at B and C respectively. P and Q are points on AB and AC respectively such that PQ touchesthe circle at R. IfAB = 11 cm, AP=7 cm and AQ = 9 cm, then find the length of PQ (in cm).

A

7

B

5

C

8

D

6