It can also be solved using Intermediate value theorem
s^ 3 + 3* s^ 2 -6*s + 2 =0
s=0: +ve
s=1 0 +ve
s=0.9 -ve value
Thus from 0 to 0.9 , there is transition from +ve to -ve , here one root exist
From 0.9 to 1 , again transition from -ve to +ve , here root exist which is 1.
(C) two solution