Simplify: \rt[3]x6y9\rt[3]{x^6 y^9}\rt[3]x6y9.
x2y3x^2 y^3x2y3
x3y3x^3 y^3x3y3
x2y6x^2 y^6x2y6
x18y27x^{18} y^{27}x18y27