Answer:
[tex]( {2x}^{3y} - 8y + 9 {x}^{3} ) - (6y + 6 {x}^{3} - 3 {x}^{3y} ) \\ = (2 + 3) {x}^{3y} + ( - 8 - 6)y + (9 - 6) {x}^{3} \\ = 5 {x}^{3y} - 14y + 3 {x}^{3 } [/tex]
