Answer:
6x^2y^3
Explanation:
6x^2y^4+18x^3y^5-12x^5y^3
Lets break each term into prime factors
6x^2y^4 =3*2*x*x*y*y*y*y
18x^3y^5 = 9*2^3y^5 = 3*3*2*x*x*x*y*y*y*y*y
12x^5y^3 = 4*3x^5y^3 = 2*2*3*x*x*x*x*x*y*y*y
Each has one 2, one 3, two x's and three y's
So the greatest common factor is
2*3*x*x*y*y*y
6x^2y^3