計圓入面ge角度..........help

1.I think you have miss some details in the question

2.as MN, NC, CB, BM are tangent of the circle at P,S, R, Q respectively,
so PN=NS,
SC=CR
RB=BQ
QM=MP

first as M,N are mid-pt of AB,AC reapcetively, MN=BC/2 (mid-pt thm)
MN=9cm

MP+PN=MN =9cm
so QM+NS = 9cm

BR+RC = BC=18cm
so BQ+SC =18cm

MB+NC =MQ+QB+NS+SC
=( QM+NS) +(BQ+SC )
=9+18=27cm

AM=MB
AN=NC
AM+AN=MB+NC =27cm
so the perimeter of triangle ABC=27+27+18=72cm