We have
P(y)=(y3−27)(y2−3y+2)=(y−3)(y2+3y+9)(y−2)(y−1),
Q(y)=(y2+3y+9)(y2−5y+6)=(y2+3y+9)(y−3)(y−2).
We observe that y−3,y−2,y−1 and y2+3y+9 are the irreducible factors each having maximum exponent equal to 1. Hence their product
(y−3)(y−2)(y2+3y+9)
is the LCM of given polynomials.