3 radical 256x9y7 - 3 radical 32x12y4 is what?

Answer 1

3*sqrt(256x^9y^7) - 3*sqrt(32x^12y^4) =
3*16*sqrt(x^8xy^6y)-3*sqrt(16*2x^12y^4)=
48x^4y^3*sqrt(xy) - 3*4*x^6y^2*sqrt(2) =
48x^4y^3*sqrt(xy) - 12x^6y^2*sqrt(2) =
12x^4y^2(4y*sqrt(xy) - x^2*sqrt(2)).

NOTE: "Sqrt" means square root.