设扇形半径为R
60/360*3.14*R^2=18.84
1/6*R^2=6
R^2=36
R=6
周长
C=60/180*3.14*6+6*2
=1/3*3.14*6+6*2
=6.28+12
=18.28厘米
答:扇形周长18.28厘米