*Hint: Before you try to factor anything, you try to see if they have a common factor.
Since -3 is a common factor, everything is divided by -3.
-6x^4y^5 - 15x^3y^2 + 9x^2y^3
-3(2x^4y^5 + 5x^3y^2 - 3x^2y^3)
Since you can still divide by x^2y^2, you do so.
-3x^2y^2 (2x^2y^3 + 5x - 3y)